Title 49—Transportation--Volume 1
PART 178—SPECIFICATIONS FOR PACKAGINGS
§ 178.1   Purpose and scope.
This part prescribes the manufacturing and testing specifications for packaging and containers used for the transportation of hazardous materials in commerce.
§ 178.2   Applicability and responsibility.
(a) Applicability. (1) The requirements of this part apply to packagings manufactured—
(i) To a DOT specification, regardless of country of manufacture; or
(ii) To a UN standard, for packagings manufactured within the United States. For UN standard packagings manufactured outside the United States, see § 173.24(d)(2) of this subchapter. For UN standard packagings for which standards are not prescribed in this part, see § 178.3(b).
(2) A manufacturer of a packaging subject to the requirements of this part is primarily responsible for compliance with the requirements of this part. However, any person who performs a function prescribed in this part shall perform that function in accordance with this part.
(b) Specification markings. When this part requires that a packaging be marked with a DOT specification or UN standard marking, marking of the packaging with the appropriate DOT or UN markings is the certification that—
(1) Except as otherwise provided in this section, all requirements of the DOT specification or UN standard, including performance tests, are met; and
(2) All functions performed by, or on behalf of, the person whose name or symbol appears as part of the marking conform to requirements specified in this part.
(c) Notification. (1) Except as specifically provided in §§ 178.337-18, 178.338-19, and 178.345-15 of this part, the manufacturer or other person certifying compliance with the requirements of this part, and each subsequent distributor of that packaging must:
(i) Notify each person to whom that packaging is transferred—
(A) Of all requirements in this part not met at the time of transfer, and
(B) With information specifying the type(s) and dimensions of the closures, including gaskets and any other components needed to ensure that the packaging is capable of successfully passing the applicable performance tests. This information must include any procedures to be followed, including closure instructions for inner packagings and receptacles, to effectively assemble and close the packaging for the purpose of preventing leakage in transportation. Closure instructions must provide for a consistent and repeatable means of closure that is sufficient to ensure the packaging is closed in the same manner as it was tested. For packagings sold or represented as being in conformance with the requirements of this subchapter applicable to transportation by aircraft, this information must include relevant guidance to ensure that the packaging, as prepared for transportation, will withstand the pressure differential requirements in § 173.27 of this subchapter.
(ii) Retain copies of each written notification for at least one year from date of issuance; and
(iii) Make copies of all written notifications available for inspection by a representative of the Department.
(2) The notification required in accordance with this paragraph (c) may be in writing or by electronic means, including e-mailed transmission or transmission on a CD or similar device. If a manufacturer or subsequent distributor of the packaging utilizes electronic means to make the required notifications, the notification must be specific to the packaging in question and must be in a form that can be printed in hard copy by the person receiving the notification.
(d) Except as provided in paragraph (c) of this section, a packaging not conforming to the applicable specifications or standards in this part may not be marked to indicate such conformance.
(e) Definitions. For the purpose of this part—
Manufacturer means the person whose name and address or symbol appears as part of the specification markings required by this part or, for a packaging marked with the symbol of an approval agency, the person on whose behalf the approval agency certifies the packaging.
Specification markings mean the packaging identification markings required by this part including, where applicable, the name and address or symbol of the packaging manufacturer or approval agency.
(f) No packaging may be manufactured or marked to a packaging specification that was in effect on September 30, 1991, and that was removed from this part 178 by a rule published in the Federal Register on December 21, 1990 and effective October 1, 1991.
§ 178.3   Marking of packagings.
(a) Each packaging represented as manufactured to a DOT specification or a UN standard must be marked on a non-removable component of the packaging with specification markings conforming to the applicable specification, and with the following:
(1) In an unobstructed area, with letters, and numerals identifying the standards or specification (e.g. UN 1A1, DOT 4B240ET, etc.).
(2) Unless otherwise specified in this part, the name and address or symbol of the packaging manufacturer or the person certifying compliance with a UN standard. Symbols, if used, must be registered with the Associate Administrator. Unless authorized in writing by the holder of the symbol, symbols must represent either the packaging manufacturer or the approval agency responsible for providing the most recent certification for the packaging through design certification testing or periodic retesting, as applicable. Duplicative symbols are not authorized.
(3) The markings must be stamped, embossed, burned, printed or otherwise marked on the packaging to provide adequate accessibility, permanency, contrast, and legibility so as to be readily apparent and understood.
(4) Unless otherwise specified, letters and numerals must be at least 12.0 mm (0.47 inches) in height except for packagings of less than or equal to 30 L (7.9 gallons) capacity for liquids or 30 kg (66 pounds) maximum net mass for solids the height must be at least 6.0 mm (0.2 inches). For packagings having a capacity of 5 L (1.3 gallons) or less or of 5 kg (11 pounds) maximum net mass, letters and numerals must be of an appropriate size.
(5) For packages with a gross mass of more than 30 kg (66 pounds), the markings or a duplicate thereof must appear on the top or on a side of the packaging.
(b) A UN standard packaging for which the UN standard is set forth in this part may be marked with the United Nations symbol and other specification markings only if it fully conforms to the requirements of this part. A UN standard packaging for which the UN standard is not set forth in this part may be marked with the United Nations symbol and other specification markings for that standard as provided in the ICAO Technical Instructions or the IMDG Code subject to the following conditions:
(1) The U.S. manufacturer must establish that the packaging conforms to the applicable provisions of the ICAO Technical Instructions (IBR, see § 171.7 of this subchapter) or the IMDG Code (IBR, see § 171.7 of this subchapter), respectively.
(2) If an indication of the name of the manufacturer or other identification of the packaging as specified by the competent authority is required, the name and address or symbol of the manufacturer or the approval agency certifying compliance with the UN standard must be entered. Symbols, if used, must be registered with the Associate Administrator.
(3) The letters “USA” must be used to indicate the State authorizing the allocation of the specification marks if the packaging is manufactured in the United States.
(c) Where a packaging conforms to more than one UN standard or DOT specification, the packaging may bear more than one marking, provided the packaging meets all the requirements of each standard or specification. Where more than one marking appears on a packaging, each marking must appear in its entirety.
(d) No person may mark or otherwise certify a packaging or container as meeting the requirements of a manufacturing special permit unless that person is the holder of or a party to that special permit, an agent of the holder or party for the purpose of marking or certification, or a third party tester.
§ 178.33   Specification 2P; inner nonrefillable metal receptacles.
§ 178.33-1   Compliance.
(a) Required in all details.
(b) [Reserved]
§ 178.33-2   Type and size.
(a) Single-trip inside containers. Must be seamless, or with seams, welded, soldered, brazed, double seamed, or swedged.
(b) The maximum capacity of containers in this class shall not exceed one liter (61.0 cubic inches). The maximum inside diameter shall not exceed 3 inches.
§ 178.33-3   Inspection.
(a) By competent inspector.
(b) [Reserved]
§ 178.33-4   Duties of inspector.
(a) To inspect material and completed containers and witness tests, and to reject defective materials or containers.
(b) [Reserved]
§ 178.33-5   Material.
(a) Uniform quality steel plate such as black plate, electro-tin plate, hot dipped tin plate, tern plate or other commercially accepted can making plate; or nonferrous metal of uniform drawing quality.
(b) Material with seams, cracks, laminations or other injurious defects not authorized.
§ 178.33-6   Manufacture.
(a) By appliances and methods that will assure uniformity of completed containers; dirt and scale to be removed as necessary; no defect acceptable that is likely to weaken the finished container appreciably; reasonably smooth and uniform surface finish required.
(b) Seams when used must be as follows:
(1) Circumferential seams: By welding, swedging, brazing, soldering, or double seaming.
(2) Side seams: By welding, brazing, or soldering.
(c) Ends: The ends shall be of pressure design.
§ 178.33-7   Wall thickness.
(a) The minimum wall thickness for any container shall be 0.007 inch.
(b) [Reserved]
§ 178.33-8   Tests.
(a) One out of each lot of 25,000 containers or less, successively produced per day shall be pressure tested to destruction and must not burst below 240 psig gauge pressure. The container tested shall be complete with end assembled.
(b) Each such 25,000 containers or less, successively produced per day, shall constitute a lot and if the test container shall fail, the lot shall be rejected or ten additional containers may be selected at random and subjected to the test under which failure occurred. These containers shall be complete with ends assembled. Should any of the ten containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design construction, finish, and quality.
§ 178.33-9   Marking.
(a) By means of printing, lithographing, embossing, or stamping, each container must be marked to show:
(1) DOT-2P.
(2) Name or symbol of person making the mark specified in paragraph (a)(1) of this section. Symbol, if used, must be registered with the Associate Administrator.
(b) [Reserved]
§ 178.33a   Specification 2Q; inner nonrefillable metal receptacles.
§ 178.33a-1   Compliance.
(a) Required in all details.
(b) [Reserved]
§ 178.33a-2   Type and size.
(a) Single-trip inside containers. Must be seamless, or with seams welded, soldered, brazed, double seamed, or swedged.
(b) The maximum capacity of containers in this class shall not exceed 1 L (61.0 cubic inches). The maximum inside diameter shall not exceed 3 inches.
§ 178.33a-3   Inspection.
(a) By competent inspector.
(b) [Reserved]
§ 178.33a-4   Duties of inspector.
(a) To inspect material and completed containers and witness tests, and to reject defective materials or containers.
(b) [Reserved]
§ 178.33a-5   Material.
(a) Uniform quality steel plate such as black plate, electrotin plate, hot dipped tinplate, ternplate or other commercially accepted can making plate; or nonferrous metal of uniform drawing quality.
(b) Material with seams, cracks, laminations or other injurious defects not authorized.
§ 178.33a-6   Manufacture.
(a) By appliances and methods that will assure uniformity of completed containers; dirt and scale to be removed as necessary; no defect acceptable that is likely to weaken the finished container appreciably; reasonably smooth and uniform surface finish required.
(b) Seams when used must be as follows:
(1) Circumferential seams. By welding, swedging, brazing, soldering, or double seaming.
(2) Side seams. By welding, brazing or soldering.
(c) Ends. The ends shall be of pressure design.
§ 178.33a-7   Wall thickness.
(a) The minimum wall thickness for any container shall be 0.008 inch.
(b) [Reserved]
§ 178.33a-8   Tests.
(a) One out of each lot of 25,000 containers or less, successively produced per day, shall be pressure tested to destruction and must not burst below 270 psig gauge pressure. The container tested shall be complete with end assembled.
(b) Each such 25,000 containers or less, successively produced per day, shall constitute a lot and if the test container shall fail, the lot shall be rejected or ten additional containers may be selected at random and subjected to the test under which failure occurred. These containers shall be complete with ends assembled. Should any of the ten containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design, construction, finish and quality.
§ 178.33a-9   Marking.
(a) By means of printing, lithographing, embossing, or stamping, each container must be marked to show:
(1) DOT-2Q.
(2) Name or symbol of person making the mark specified in paragraph (a)(1) of this section. Symbol, if used, must be registered with the Associate Administrator.
(b) [Reserved]
§ 178.33b   Specification 2S; inner nonrefillable plastic receptacles.
§ 178.33b-1   Compliance.
(a) Required in all details.
(b) [Reserved]
§ 178.33b-2   Type and size.
(a) Single-trip inside containers.
(b) The maximum capacity of containers in this class shall not exceed one liter (61.0 cubic inches). The maximum inside diameter shall not exceed 3 inches.
§ 178.33b-3   Inspection.
(a) By competent inspector.
(b) [Reserved]
§ 178.33b-4   Duties of inspector.
(a) To inspect material and completed containers and witness tests, and to reject defective materials or containers.
(b) [Reserved]
§ 178.33b-5   Material.
(a) The receptacles must be constructed of polyethylene terephthalate (PET), polyethylene napthalate (PEN), polyamide (Nylon) or a blend of PET, PEN, ethyl vinyl alcohol (EVOH) and/or Nylon.
(b) Material with seams, cracks, laminations or other injurious defects are forbidden.
§ 178.33b-6   Manufacture.
(a) Each container must be manufactured by thermoplastic processes that will assure uniformity of the completed container. No used material other than production residues or regrind from the same manufacturing process may be used. The packaging must be adequately resistant to aging and to degradation caused either by the substance contained or by ultraviolet radiation.
(b) [Reserved]
§ 178.33b-7   Design qualification test.
(a) Drop testing. (1) To ensure that creep does not affect the ability of the container to retain the contents, each new design must be drop tested as follows: Three groups of twenty-five filled containers must be dropped from 1.8 m (5.9 ft) on to a rigid, non-resilient, flat and horizontal surface. One group must be conditioned at 38 °C (100 °F) for 26 weeks, the second group for 100 hours at 50 °C (122 °F) and the third group for 18 hours at 55 °C (131 °F), prior to performing the drop test. The closure, or sealing component of the container, must not be protected during the test. The orientation of the test container at drop must be statistically random, but direct impact on the valve or valve closure must be avoided.
(2) Criteria for passing the drop test: The containers must not break or leak.
(b) Design qualification testing must be completed if the design is manufactured with a new mold or if there is any change in the properties of the material of construction.
§ 178.33b-8   Production tests.
(a) Burst Testing. (1) One out of each lot of 5,000 containers or less, successively produced per day must be pressure tested to destruction and must not burst below 240 psig. The container tested must be complete as intended for transportation.
(2) Each such 5,000 containers or less, successively produced per day, shall constitute a lot and if the test container shall fail, the lot shall be rejected or ten additional containers may be selected at random and subjected to the test under which failure occurred. These containers shall be complete as intended for transportation. Should any of the ten containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design construction, finish, and quality.
(b) [Reserved]
§ 178.33b-9   Marking.
(a) Each container must be clearly and permanently marked to show:
(1) DOT-2S.
(2) Name or symbol of person making the mark specified in paragraph (a)(1) of this section. Symbol, if used, must be registered with the Associate Administrator.
(b) [Reserved]
§ 178.33c   Specification 2P; inner nonrefillable metal receptacle variation.
§ 178.33c-1   Compliance.
Required in all details.
§ 178.33c-2   Variation.
Notwithstanding the variation provided in this section, each container must otherwise conform to a DOT 2P container in accordance with § 178.33. The following conditions also apply under Variation 1—
(a) Manufacture. Side seams: not permitted. Ends: The ends shall be designed to withstand pressure and be equipped with a pressure relief system (e.g., rim-venting release or a dome expansion device) designed to function prior to bursting of the container.
(b) Tests. (1) One out of each lot of 25,000 containers or less, successively produced per day complete with ends assembled (and without a pressure relief system assembled) shall be pressure tested to destruction at gauge pressure and must not burst below 240 psig. For containers with a pressure relief system as described in paragraph (a) of this section and assembled, failure at a location other than the pressure relief system will reject the lot. For containers with an end expansion device, the lot must be rejected if the container bursts prior to buckling of the device.
(2) Each such 25,000 containers or less, successively produced per day, shall constitute a lot and if the test container(s) shall fail, the lot shall be rejected. Otherwise, ten (10) additional containers of each container design produced may be selected at random and subjected to the test. These containers shall be complete with ends assembled. Should any of the containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design construction, finish, and quality.
(c) Marking. By means of printing, lithographing, embossing, or stamping, each container must be marked:
(1) DOT-2P1.
(2) With the name or symbol of the person making the mark. A symbol, if used, must be registered with the Associate Administrator.
§ 178.33d   Specification 2Q; inner nonrefillable metal receptacle variations.
§ 178.33d-1   Compliance.
Required in all details.
§ 178.33d-2   Variation 1.
Notwithstanding the variation provided in this paragraph, each container must otherwise conform to a DOT 2Q container in accordance with § 178.33a. The following conditions also apply under Variation 1—
(a) Type and size. The maximum capacity of containers in this class may not exceed 0.40 L (24.4 cubic inches). The maximum inside diameter shall not exceed 2.1 inches.
(b) Manufacture. Ends: The top of the container must be designed with a pressure relief system consisting of radial scores on the top seam(s). The bottom of the container must be designed to buckle at a pressure greater than the pressure at which the top buckles and vents.
(c) Wall thickness. The minimum wall thickness for any container shall be 0.0085 inches.
(d) Tests. (1) Two containers (one without a pressure relief system and one with) out of each lot of 25,000 or less, successively produced per day shall be pressure tested to destruction at gauge pressure. The container without a pressure relief system must not burst below 320 psig. The container assembled with a pressure relief system as described in paragraph (b) of this section must be tested to destruction. The bottom of the container must buckle at a pressure greater than the pressure at which the top buckles and vents.
(2) Each such 25,000 containers or less, successively produced per day, shall constitute a lot and if the test container(s) shall fail, the lot shall be rejected. Otherwise, ten (10) additional pairs of containers may be selected at random and subjected to the test under which failure occurred. Should any of the containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design construction, finish, and quality.
(e) Marking. By means of printing, lithographing, embossing, or stamping, each container must be marked:
(1) DOT-2Q1.
(2) With the name or symbol of the person making the mark. A symbol, if used, must be registered with the Associate Administrator.
§ 178.33d-3   Variation 2.
Notwithstanding the variation provided in this paragraph, each container must otherwise conform to a DOT 2Q container in accordance with § 178.33a. The following conditions also apply under Variation 2—
(a) Manufacture. Ends: The ends shall be designed to withstand pressure and the container equipped with a pressure relief system (e.g., rim-venting release or a dome expansion device) designed to buckle prior to the burst of the container.
(b) Tests. (1) One out of each lot of 25,000 containers or less, successively produced per day shall be pressure tested to destruction at gauge pressure and must not burst below 270 psig. For containers with a pressure relief system as described in paragraph (a) of this section and assembled, failure at a location other than the pressure relief system will reject the lot.
(2) Each such 25,000 containers or less, successively produced per day, shall constitute a lot and if the test container(s) shall fail, the lot shall be rejected. Otherwise, ten (10) additional containers of each container design produced may be selected at random and subjected to the test. These containers shall be complete with ends assembled. Should any of the containers thus tested fail, the entire lot must be rejected. All containers constituting a lot shall be of like material, size, design construction, finish, and quality.
(c) Marking. By means of printing, lithographing, embossing, or stamping, each container must be marked:
(1) DOT-2Q2.
(2) With the name or symbol of the person making the mark. A symbol, if used, must be registered with the Associate Administrator.
§ 178.35   General requirements for specification cylinders.
(a) Compliance. Compliance with the requirements of this subpart is required in all details.
(b) Inspections and analyses. Chemical analyses and tests required by this subchapter must be made within the United States, unless otherwise approved in writing by the Associate Administrator, in accordance with subpart I of part 107 of this chapter. Inspections and verification must be performed by—
(1) An independent inspection agency approved in writing by the Associate Administrator, in accordance with subpart I of part 107 of this chapter; or
(2) For DOT Specifications 3B, 3BN, 3E, 4B, 4BA, 4B240ET, 4AA480, 4L, 8, 8AL, 4BW, 4E, 4D (with a water capacity less than 1,100 cubic inches) and Specification 39 (with a marked service pressure 900 psig or lower), and manufactured within the United States, a competent inspector of the manufacturer.
(c) Duties of inspector. The inspector shall determine that each cylinder made is in conformance with the applicable specification. Inspections shall conform to CGA C-11 (IBR, see § 171.7 of this subchapter) except as otherwise specified in the applicable specification.
(1) Seamless cylinders. Seamless cylinders shall be inspected in accordance with Section 5 of CGA C-11. For cylinders made by the billet-piercing process, billets must be inspected and shown to be free from piping (laminations), cracks, excessive segregation and other injurious defects after parting or, when applicable, after nick and cold break.
(2) Welded cylinders. Welded cylinders shall be inspected in accordance with Section 6 of CGA C-11. Note: The recommended locations for test specimens are depicted in Figures 1 through 5 in appendix A to subpart C of part 178.
(3) Non-refillable cylinders. Non-refillable cylinders shall be inspected in accordance with Section 7 of CGA C-11
(4) Inspector's report. The inspector shall prepare a report containing, at a minimum, the applicable information listed in CGA C-11. Any additional information or markings that are required by the applicable specification must be shown on the test report. The signature of the inspector on the reports certifies that the processes of manufacture and heat treatment of cylinders were observed and found satisfactory. The inspector must furnish the completed test reports required by this subpart to the maker of the cylinder and, upon request, to the purchaser. The test report must be retained by the inspector for 15 years from the original test date of the cylinder.
(d) Defects and attachments. Cylinders must conform to the following:
(1) A cylinder may not be constructed of material with seams, cracks or laminations, or other injurious defects.
(2) Metal attachments to cylinders must have rounded or chamfered corners or must be protected in such a manner as to prevent the likelihood of causing puncture or damage to other hazardous materials packages. This requirement applies to anything temporarily or permanently attached to the cylinder, such as metal skids.
(e) Safety devices. Pressure relief devices and protection for valves, safety devices, and other connections, if applied, must be as required or authorized by the appropriate specification, and as required in § 173.301 of this subchapter.
(f) Markings. Markings on a DOT Specification cylinder must conform to applicable requirements.
(1) Each cylinder must be marked with the following information:
(i) The DOT specification marking must appear first, followed immediately by the service pressure. For example, DOT-3A1800.
(ii) The serial number must be placed just below or immediately following the DOT specification marking.
(iii) A symbol (letters) must be placed just below, immediately before or following the serial number. Other variations in sequence of markings are authorized only when necessitated by a lack of space. The symbol and numbers must be those of the manufacturer. The symbol must be registered with the Associate Administrator; duplications are not authorized.
(iv) The inspector's official mark and date of test (such as 5-95 for May 1995) must be placed near the serial number. This information must be placed so that dates of subsequent tests can be easily added. An example of the markings prescribed in this paragraph (f)(1) is as follows:
Or;
(2) Additional required marking must be applied to the cylinder as follows:
(i) The word “spun” or “plug” must be placed near the DOT specification marking when an end closure in the finished cylinder has been welded by the spinning process, or effected by plugging.
(ii) As prescribed in specification 3HT (§ 178.44) or 3T (§ 178.45), if applicable.
(3) Marking exceptions. A DOT 3E cylinder is not required to be marked with an inspector's mark or a serial number.
(4) Unless otherwise specified in the applicable specification, the markings on each cylinder must be stamped plainly and permanently on the shoulder, top head, or neck.
(5) The size of each marking must be at least 0.25 inch or as space permits.
(6) Other markings are authorized provided they are made in low stress areas other than the side wall and are not of a size and depth that will create harmful stress concentrations. Such marks may not conflict with any DOT required markings.
(7) Marking exceptions. A DOT 8 or 8AL cylinder is not required to be marked with the service pressure.
(8) Tare weight or mass weight, and water capacity marking. DOT-specification 4B, 4BA, 4BW, and 4E cylinders used in liquefied compressed gas service manufactured after December 28, 2022, must be marked with the tare weight or mass weight. Additionally, the cylinder must be permanently marked with the water capacity. The owner of the cylinder must ensure it is marked with the following information, as applicable:
(i) Tare weight. The tare weight for a cylinder 25 pounds or less at the time of manufacture, with a lower tolerance of 3 percent and an upper tolerance of 1 percent; or for a cylinder exceeding 25 pounds at the time of manufacture, with a lower tolerance of 2 percent and an upper tolerance of 1 percent. The tare weight marking must be the actual weight of the fully assembled cylinder, including the valve(s) and other permanently affixed appurtenances. Removable protective cap(s) or cover(s) must not be included in the cylinder tare weight. Tare weight shall be abbreviated “TW”; or
(ii) Mass weight. The mass weight for a cylinder 25 pounds or less at the time of manufacture, with a lower tolerance of 3 percent and an upper tolerance of 1 percent; or the mass weight marking for a cylinder exceeding 25 pounds at the time of manufacture, with a lower tolerance of 2 percent and an upper tolerance of 1 percent. The mass weight marking must be the actual weight of the fully assembled cylinder, excluding valve(s) and removable protective cap(s) or cover(s). Mass weight shall be abbreviated “MW”; and
(iii) Water capacity. The water capacity for a cylinder 25 pounds water capacity or less, with a tolerance of minus 1 percent and no upper tolerance; or for a cylinder exceeding 25 pounds water capacity, with a tolerance of minus 0.5 percent and no upper tolerance. The marked water capacity of the cylinder must be the capacity of the cylinder at the time of manufacture. Water capacity shall be abbreviated “WC”.
(g) Manufacturer's reports. At or before the time of delivery to the purchaser, the cylinder manufacturer must have all completed certification documents listed in CGA C-11. The manufacturer of the cylinders must retain the reports required by this subpart for 15 years from the original test date of the cylinder.
§ 178.36   Specification 3A and 3AX seamless steel cylinders.
(a) Type size and service pressure. In addition to the requirements of § 178.35, cylinders must conform to the following:
(1) A DOT-3A cylinder is a seamless steel cylinder with a water capacity (nominal) not over 1,000 pounds and a service pressure of at least 150 psig.
(2) A DOT-3AX is a seamless steel cylinder with a water capacity not less than 1,000 pounds and a service pressure of at least 500 psig, conforming to the following requirements:
(i) Assuming the cylinder is to be supported horizontally at its two ends only and to be uniformly loaded over its entire length consisting of the weight per unit of length of the straight cylindrical portion filled with water and compressed to the specified test pressure; the sum of two times the maximum tensile stress in the bottom fibers due to bending, plus that in the same fibers (longitudinal stress), due to hydrostatic test may not exceed 80 percent of the minimum yield strength of the steel at such maximum stress. Wall thickness must be increased when necessary to meet the requirement.
(ii) To calculate the maximum longitudinal tensile stress due to bending, the following formula must be used:
(iii) To calculate the maximum longitudinal tensile stress due to hydrostatic test pressure, the following formula must be used:
(b) Steel. Open-hearth or electric steel of uniform quality must be used. Content percent may not exceed the following: Carbon, 0.55; phosphorous, 0.045; sulphur, 0.050.
(c) Identification of material. Material must be identified by any suitable method, except that plates and billets for hot-drawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No fissure or other defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. If not originally free from such defects, the surface may be machined or otherwise treated to eliminate these defects. The thickness of the bottoms of cylinders welded or formed by spinning is, under no condition, to be less than two times the minimum wall thickness of the cylindrical shell; such bottom thicknesses must be measured within an area bounded by a line representing the points of contact between the cylinder and floor when the cylinder is in a vertical position.
(e) Welding or brazing. Welding or brazing for any purpose whatsoever is prohibited except as follows:
(1) Welding or brazing is authorized for the attachment of neckrings and footrings which are non-pressure parts and only to the tops and bottoms of cylinders having a service pressure of 500 psig or less. Cylinders, neckrings, and footrings must be made of weldable steel, the carbon content of which may not exceed 0.25 percent except in the case of 4130X steel which may be used with proper welding procedures.
(2) As permitted in paragraph (d) of this section.
(3) Cylinders used solely in anhydrous ammonia service may have a 1/2 inch diameter bar welded within their concave bottoms.
(f) Wall thickness. For cylinders with service pressure less than 900 psig, the wall stress may not exceed 24,000 psig. A minimum wall thickness of 0.100 inch is required for any cylinder over 5 inches outside diameter. Wall stress calculation must be made by using the following formula:
(g) Heat treatment. The completed cylinder must be uniformly and properly heat-treated prior to tests.
(h) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads are required on openings.
(1) Threads must be clean cut, even, without checks, and to gauge.
(2) Taper threads, when used, must be of length not less than as specified for American Standard taper pipe threads.
(3) Straight threads having at least 6 engaged threads are authorized. Straight threads must have a tight fit and calculated shear strength of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to a minimum of 5/3 times service pressure.
(3) The minimum test pressure must be maintained for at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent, volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(j) Flattening test. A flattening test must be performed on one cylinder taken at random out of each lot of 200 or less, by placing the cylinder between wedge shaped knife edges having a 60° included angle, rounded to 1/2 -inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to knife edges during the test. For lots of 30 or less, flattening tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(k) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material as follows:
(1) The test is required on 2 specimens cut from 1 cylinder taken at random out of each lot of 200 or less. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(2) Specimens must conform to the following:
(i) Gauge length of 8 inches with a width of not over 1 1/2 inches, a gauge length of 2 inches with a width of not over 1 1/2 inches, or a gauge length of at least 24 times thickness with width not over 6 times thickness is authorized when cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within 1 inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2-percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psig and the strain indicator reading must be set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(l) Acceptable results for physical and flattening tests. Either of the following is an acceptable result:
(1) An elongation at least 40 percent for a 2-inch gauge length or at least 20 percent in other cases and yield strength not over 73 percent of tensile strength. In this instance, the flattening test is not required.
(2) An elongation at least 20 percent for a 2-inch gauge length or 10 percent in other cases and a yield strength not over 73 percent of tensile strength. In this instance, the flattening test is required, without cracking, to 6 times the wall thickness.
(m) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by gas or air pressure after the bottom has been cleaned and is free from all moisture subject to the following conditions and limitations:
(1) Pressure, approximately the same as but no less than service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least 1 minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Except as provided in paragraph (n) of this section, a cylinder that is leaking must be rejected.
(2) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(3) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(4) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, the manufacturer should design the test apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(n) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding or spinning is not authorized. Spun cylinders rejected under the provisions of paragraph (m) of this section may be removed from the spun cylinder category by drilling to remove defective material, tapping and plugging.
§ 178.37   Specification 3AA and 3AAX seamless steel cylinders.
(a) Type, size and service pressure. In addition to the requirements of § 178.35, cylinders must conform to the following:
(1) A DOT-3AA cylinder is a seamless steel cylinder with a water capacity (nominal) of not over 1,000 pounds and a service pressure of at least 150 psig.
(2) A DOT-3AAX cylinder is a seamless steel cylinder with a water capacity of not less than 1,000 pounds and a service pressure of at least 500 psig, conforming to the following requirements:
(i) Assuming the cylinder is to be supported horizontally at its two ends only and to be uniformly loaded over its entire length consisting of the weight per unit of length of the straight cylindrical portion filled with water and compressed to the specified test pressure; the sum of two times the maximum tensile stress in the bottom fibers due to bending, plus that in the same fibers (longitudinal stress), due to hydrostatic test pressure may not exceed 80 percent of the minimum yield strength of the steel at such maximum stress. Wall thickness must be increased when necessary to meet the requirement.
(ii) To calculate the maximum tensile stress due to bending, the following formula must be used:
(iii) To calculate the maximum longitudinal tensile stress due to hydrostatic test pressure, the following formula must be used:
(b) Authorized steel. Open-hearth, basic oxygen, or electric steel of uniform quality must be used. A heat of steel made under the specifications in table 1 of this paragraph (b), check chemical analysis of which is slightly out of the specified range, is acceptable, if satisfactory in all other respects, provided the tolerances shown in table 2 of this paragraph (b) are not exceeded. When a carbon-boron steel is used, a hardenability test must be performed on the first and last ingot of each heat of steel. The results of this test must be recorded on the Record of Chemical Analysis of Material for Cylinders required by § 178.35. This hardness test must be made 5/16 -inch from the quenched end of the Jominy quench bar and the hardness must be at least Rc 33 and no more than Rc 53. The following chemical analyses are authorized:
Table 1—Authorized Materials
Note 1: This designation may not be restrictive and the commercial steel is limited in analysis as shown in this table.
Table 2—Check Analysis Tolerances
1 Rephosphorized steels not subject to check analysis for phosphorus.
(c) Identification of material. Material must be identified by any suitable method except that plates and billets for hot-drawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No fissure or other defects is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. If not originally free from such defects, the surface may be machined or otherwise treated to eliminate these defects. The thickness of the bottoms of cylinders welded or formed by spinning is, under no condition, to be less than two times the minimum wall thickness of the cylindrical shell; such bottom thicknesses must be measured within an area bounded by a line representing the points of contact between the cylinder and floor when the cylinder is in a vertical position.
(e) Welding or brazing. Welding or brazing for any purpose whatsoever is prohibited except as follows:
(1) Welding or brazing is authorized for the attachment of neckrings and footrings which are non-pressure parts, and only to the tops and bottoms of cylinders having a service pressure of 500 psig or less. Cylinders, neckrings, and footrings must be made of weldable steel, the carbon content of which may not exceed 0.25 percent except in the case of 4130X steel which may be used with proper welding procedure.
(2) As permitted in paragraph (d) of this section.
(f) Wall thickness. The thickness of each cylinder must conform to the following:
(1) For cylinders with a service pressure of less than 900 psig, the wall stress may not exceed 24,000 psi. A minimum wall thickness of 0.100 inch is required for any cylinder with an outside diameter of over 5 inches.
(2) For cylinders with service pressure of 900 psig or more the minimum wall must be such that the wall stress at the minimum specified test pressure may not exceed 67 percent of the minimum tensile strength of the steel as determined from the physical tests required in paragraphs (k) and (l) of this section and must be not over 70,000 psi.
(3) Calculation must be made by the formula:
(g) Heat treatment. The completed cylinders must be uniformly and properly heat treated prior to tests. Heat treatment of cylinders of the authorized analyses must be as follows:
(1) All cylinders must be quenched by oil, or other suitable medium except as provided in paragraph (g)(5) of this section.
(2) The steel temperature on quenching must be that recommended for the steel analysis, but may not exceed 1750 °F.
(3) All steels must be tempered at a temperature most suitable for that steel.
(4) The minimum tempering temperature may not be less than 1000 °F except as noted in paragraph (g)(6) of this section.
(5) Steel 4130X may be normalized at a temperature of 1650 °F instead of being quenched and cylinders so normalized need not be tempered.
(6) Intermediate manganese steels may be tempered at temperatures not less than 1150 °F., and after heat treating each cylinder must be submitted to a magnetic test to detect the presence of quenching cracks. Cracked cylinders must be rejected and destroyed.
(7) Except as otherwise provided in paragraph (g)(6) of this section, all cylinders, if water quenched or quenched with a liquid producing a cooling rate in excess of 80 percent of the cooling rate of water, must be inspected by the magnetic particle, dye penetrant or ultrasonic method to detect the presence of quenching cracks. Any cylinder designed to the requirements for specification 3AA and found to have a quenching crack must be rejected and may not be requalified. Cylinders designed to the requirements for specification 3AAX and found to have cracks must have cracks removed to sound metal by mechanical means. Such specification 3AAX cylinders will be acceptable if the repaired area is subsequently examined to assure no defect, and it is determined that design thickness requirements are met.
(h) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads are required on openings.
(1) Threads must be clean cut, even, without checks, and to gauge.
(2) Taper threads, when used, must be of a length not less than as specified for American Standard taper pipe threads.
(3) Straight threads having at least 6 engaged threads are authorized. Straight threads must have a tight fit and a calculated shear strength of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to a minimum of 5/3 times service pressure.
(3) The minimum test pressure must be maintained for at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent, volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(j) Flattening test. A flattening test must be performed on one cylinder, taken at random out of each lot of 200 or fewer, by placing the cylinder between wedge shaped knife edges, having a 60-degree included angle, rounded to 1/2 -inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to the knife edges during the test. For lots of 30 or fewer, flattening tests are authorized to be made on a ring at least eight (8) inches long, cut from each cylinder and subjected to the same heat treatment as the finished cylinder. Cylinders may be subjected to a bend test in lieu of the flattening test. Two bend test specimens must be taken in accordance with ISO 9809-1:2019(E) or ASTM E290 (IBR, see § 171.7 of this subchapter), and must be subjected to the bend test specified therein.
(k) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material as follows:
(1) The test is required on 2 specimens cut from 1 cylinder taken at random out of each lot of 200 or less. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to the same heat treatment as the finished cylinder.
(2) Specimens must conform to the following:
(i) Gauge length of 8 inches with a width of not over 1 1/2 inches, a gauge length of 2 inches with a width of not over 1 1/2 inches, or a gauge length of at least 24 times the thickness with width not over 6 times thickness when the thickness of the cylinder wall is not over 3/16 inch.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within 1 inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi, the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(l) Acceptable results for physical, flattening and bend tests. An acceptable result for physical and flattening tests is elongation of at least 20 percent for 2 inches of gauge length or at least 10 percent in other cases. Flattening is required, without cracking, to 6 times the wall thickness of the cylinder. An acceptable result for the alternative bend test is no crack when the cylinder is bent inward around the mandrel until the interior edges are not further apart than the diameter of the mandrel.
(m) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by gas or air pressure after the bottom has been cleaned and is free from all moisture. Pressure, approximately the same as but no less than the service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least one minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Except as provided in paragraph (n) of this section, a cylinder must be rejected if there is any leaking.
(1) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(2) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(3) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, the manufacturer should design the test apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(n) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding or spinning is not authorized. Spun cylinders rejected under the provision of paragraph (m) of this section may be removed from the spun cylinder category by drilling to remove defective material, tapping and plugging.
§ 178.38   Specification 3B seamless steel cylinders.
(a) Type, size, and service pressure. A DOT 3B cylinder is seamless steel cylinder with a water capacity (nominal) of not over 1,000 pounds and a service pressure of at least 150 to not over 500 psig.
(b) Steel. Open-hearth or electric steel of uniform quality must be used. Content percent may not exceed the following: carbon, 0.55; phosphorus, 0.045; sulphur, 0.050.
(c) Identification of material. Material must be identified by any suitable method except that plates and billets for hot-drawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No fissure or other defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. If not originally free from such defects, the surface may be machined or otherwise treated to eliminate these defects. The thickness of the bottoms of cylinders welded or formed by spinning is, under no condition, to be less than two times the minimum wall thickness of the cylindrical shell; such bottom thicknesses to be measured within an area bounded by a line representing the points of contact between the cylinder and floor when the cylinder is in a vertical position.
(e) Welding or brazing. Welding or brazing for any purpose whatsoever is prohibited except as follows:
(1) Welding or brazing is authorized for the attachment of neckrings and footrings which are non-pressure parts, and only to the tops and bottoms of cylinders having a service pressure of 500 psig or less. Cylinders, neckrings, and footrings must be made of weldable steel, carbon content of which may not exceed 0.25 percent except in the case of 4130X steel which may be used with proper welding procedure.
(2) As permitted in paragraph (d) of this section.
(f) Wall thickness. The wall stress may not exceed 24,000 psi. The minimum wall thickness is 0.090 inch for any cylinder with an outside diameter of 6 inches. Calculation must be made by the following formula:
(g) Heat treatment. The completed cylinders must be uniformly and properly heat-treated prior to tests.
(h) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads, conforming to the following, are required on all openings:
(1) Threads must be clean cut, even, without checks, and to gauge.
(2) Taper threads when used, must be of a length not less than as specified for American Standard taper pipe threads.
(3) Straight threads having at least 4 engaged threads are authorized. Straight threads must have a tight fit, and calculated shear strength at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as defined in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Cylinders must be tested as follows:
(i) Each cylinder to at least two (2) times its service pressure; or
(ii) One (1) cylinder out of each lot of 200 or fewer to at least three (3) times its service pressure. When one (1) cylinder out of each lot of 200 or less is tested to at least 3 times service pressure, the balance of the lot must be pressure tested by the proof pressure, water-jacket or direct expansion test method as prescribed in CGA C-1. The cylinders must be subjected to at least 2 times service pressure and show no defect. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2, as appropriate. Determination of expansion properties is not required.
(3) When each cylinder is tested to the minimum test pressure, the minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(j) Flattening test. A flattening test must be performed on one cylinder taken at random out of each lot of 200 or less, by placing the cylinder between wedge shaped knife edges having a 60° included angle, rounded to 1/2 -inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to knife edges during the test. For lots of 30 or less, flattening tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(k) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material, as follows:
(1) The test is required on 2 specimens cut from 1 cylinder taken at random out of each lot of 200 or less. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(2) Specimens must conform to the following:
(i) Gauge length of 8 inches with a width of not over 1 1/2 inches; or a gauge length of 2 inches with a width of not over 1 1/2 inches; or a gauge length at least 24 times the thickness with a width not over 6 times thickness is authorized when a cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi, and the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(l) Acceptable results for physical and flattening tests. Either of the following is an acceptable result:
(1) An elongation of at least 40 percent for a 2-inch gauge length or at least 20 percent in other cases and yield strength not over 73 percent of tensile strength. In this instance, the flattening test is not required.
(2) An elongation of at least 20 percent for a 2-inch gauge length or 10 percent in other cases and yield strength not over 73 percent of tensile strength. Flattening is required, without cracking, to 6 times the wall thickness.
(m) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by gas or air pressure after the bottom has been cleaned and is free from all moisture, subject to the following conditions and limitations:
(1) Pressure, approximately the same as but no less than service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least one minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Except as provided in paragraph (n) of this section, a cylinder must be rejected if there is any leaking.
(2) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(3) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(4) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, he should design his apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(n) Rejected cylinders. Reheat treatment of rejected cylinders is authorized. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding or spinning is not authorized. Spun cylinders rejected under the provisions of paragraph (m) of this section may be removed from the spun cylinder category by drilling to remove defective material, tapping and plugging.
(o) Marking. Markings may be stamped into the sidewalls of cylinders having a service pressure of 150 psig if all of the following conditions are met:
(1) Wall stress at test pressure may not exceed 24,000 psi.
(2) Minimum wall thickness must be not less than 0.090 inch.
(3) Depth of stamping must be no greater than 15 percent of the minimum wall thickness, but may not exceed 0.015 inch.
(4) Maximum outside diameter of cylinder may not exceed 5 inches.
(5) Carbon content of cylinder may not exceed 0.25 percent. If the carbon content exceeds 0.25 percent, the complete cylinder must be normalized after stamping.
(6) Stamping must be adjacent to the top head.
§ 178.39   Specification 3BN seamless nickel cylinders.
(a) Type, size and service pressure. A DOT 3BN cylinder is a seamless nickel cylinder with a water capacity (nominal) not over 125 pounds water capacity (nominal) and a service pressure at least 150 to not over 500 psig.
(b) Nickel. The percentage of nickel plus cobalt must be at least 99.0 percent.
(c) Identification of material. The material must be identified by any suitable method except that plates and billets for hot-drawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. Cylinders closed in by spinning process are not authorized.
(e) Welding or brazing. Welding or brazing for any purpose whatsoever is prohibited except that welding is authorized for the attachment of neckrings and footrings which are nonpressure parts, and only to the tops and bottoms of cylinders. Neckrings and footrings must be of weldable material, the carbon content of which may not exceed 0.25 percent. Nickel welding rod must be used.
(f) Wall thickness. The wall stress may not exceed 15,000 psi. A minimum wall thickness of 0.100 inch is required for any cylinder over 5 inches in outside diameter. Wall stress calculation must be made by using the following formula:
(g) Heat treatment. The completed cylinders must be uniformly and properly heat-treated prior to tests.
(h) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads conforming to the following are required on openings:
(1) Threads must be clean cut, even, without checks, and to gauge.
(2) Taper threads, when used, to be of length not less than as specified for American Standard taper pipe threads.
(3) Straight threads having at least 6 engaged threads are authorized. Straight threads must have a tight fit and a calculated shear strength of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to a minimum of at least two (2) times its service pressure.
(3) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(j) Flattening test. A flattening test must be performed on one cylinder taken at random out of each lot of 200 or less, by placing the cylinder between wedge shaped knife edges having a 60° included angle, rounded to 1/2 -inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to knife edges during the test. For lots of 30 or less, flattening tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(k) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material, as follows:
(1) The test is required on 2 specimens cut from 1 cylinder taken at random out of each lot of 200 or less. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(2) Specimens must conform to the following:
(i) A gauge length of 8 inches with a width of not over 1 1/2 inches, a gauge length of 2 inches with a width of not over 1 1/2 inches, or a gauge length of at least 24 times the thickness with a width not over 6 times thickness is authorized when a cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi, and the strain indicator reading must be set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(l) Acceptable results for physical and flattening tests. Either of the following is an acceptable result:
(1) An elongation of at least 40 percent for a 2 inch gauge length or at least 20 percent in other cases and yield point not over 50 percent of tensile strength. In this instance, the flattening test is not required.
(2) An elongation of at least 20 percent for a 2 inch gauge length or 10 percent in other cases and a yield point not over 50 percent of tensile strength. Flattening is required, without cracking, to 6 times the wall thickness.
(m) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding is not authorized.
§ 178.42   Specification 3E seamless steel cylinders.
(a) Type, size, and service pressure. A DOT 3E cylinder is a seamless steel cylinder with an outside diameter not greater than 2 inches nominal, a length less than 2 feet and a service pressure of 1,800 psig.
(b) Steel. Open-hearth or electric steel of uniform quality must be used. Content percent may not exceed the following: Carbon, 0.55; phosphorus, 0.045; sulphur, 0.050.
(c) Identification of steel. Materials must be identified by any suitable method.
(d) Manufacture. Cylinders must be manufactured by best appliances and methods. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. The thickness of the spun bottom is, under no condition, to be less than two times the minimum wall thickness of the cylindrical shell; such bottom thickness must be measured within an area bounded by a line representing the points of contact between the cylinder and floor when the cylinder is in a vertical position.
(e) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads conforming to the following are required on openings.
(1) Threads must be clean cut, even, without checks, and to gauge.
(2) Taper threads, when used, must be of length not less than as specified for American Standard taper pipe threads.
(3) Straight threads having at least 4 engaged threads are authorized. Straight threads must have a tight fit and a calculated shear strength of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(f) Pressure testing. Cylinders must be tested as follows:
(1) One cylinder out of each lot of 500 or fewer must be subjected to a hydrostatic test pressure of 6,000 psig or higher.
(2) The cylinder referred to in paragraph (f)(1) of this section must burst at a pressure higher than 6,000 psig without fragmenting or otherwise showing lack of ductility, or must hold a pressure of 12,000 psig for 30 seconds without bursting. In which case, it must be subjected to a flattening test without cracking to six times wall thickness between knife edges, wedge shaped 60 degree angle, rounded out to a 1/2 inch radius. The inspector's report must be suitably changed to show results of latter alternate and flattening test. The testing equipment must be calibrated as prescribed in CGA C-1 (IBR, see § 171.7 of this subchapter). All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(3) The remaining cylinders of the lot must be pressure tested by the proof pressure water-jacket or direct expansion test method as prescribed in CGA C-1. Cylinders must be examined under pressure of at least 3,000 psig and not to exceed 4,500 psig and show no defect. Cylinders tested at a pressure in excess of 3,600 psig must burst at a pressure higher than 7,500 psig when tested as specified in paragraph (f)(2) of this section. The pressure must be maintained for at least 30 seconds and sufficiently longer to ensure complete examination. The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2, as appropriate. Determination of expansion properties is not required.
(g) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by gas or air pressure after the bottom has been cleaned and is free from all moisture subject to the following conditions and limitations:
(1) A pressure, approximately the same as but not less than the service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least one minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Accept as provided in paragraph (h) of this section, a cylinder must be rejected if there is any leakage.
(2) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(3) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(4) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, the manufacturer shall design the test apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(h) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding or spinning is not authorized. Spun cylinders rejected under the provisions of paragraph (g) of this section may be removed from the spun cylinder category by drilling to remove defective material, tapping and plugging.
(i) Marking. Markings required by § 178.35 must be stamped plainly and permanently on the shoulder, top head, neck or sidewall of each cylinder.
§ 178.44   Specification 3HT seamless steel cylinders for aircraft use.
(a) Type, size and service pressure. A DOT 3HT cylinder is a seamless steel cylinder with a water capacity (nominal) of not over 150 pounds and a service pressure of at least 900 psig.
(b) Authorized steel. Open hearth or electric furnace steel of uniform quality must be used. A heat of steel made under the specifications listed in Table 1 in this paragraph (b), a check chemical analysis that is slightly out of the specified range is acceptable, if satisfactory in all other respects, provided the tolerances shown in Table 2 in this paragraph (b) are not exceeded. The maximum grain size shall be 6 or finer. The grain size must be determined in accordance with ASTM E 112-88 (IBR, see § 171.7 of this subchapter). Steel of the following chemical analysis is authorized:
Table 1—Authorized Materials
Table 2—Check Analysis Tolerances
1 Rephosphorized steels not subject to check analysis for phosphorus.
(c) Identification of material. Material must be identified by any suitable method. Steel stamping of heat identifications may not be made in any area which will eventually become the side wall of the cylinder. Depth of stamping may not encroach upon the minimum prescribed wall thickness of the cylinder.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No fissure or other defect is permitted that is likely to weaken the finished container appreciably. The general surface finish may not exceed a roughness of 250 RMS. Individual irregularities such as draw marks, scratches, pits, etc., should be held to a minimum consistent with good high stress pressure vessel manufacturing practices. If the cylinder is not originally free of such defects or does not meet the finish requirements, the surface may be machined or otherwise treated to eliminate these defects. The point of closure of cylinders closed by spinning may not be less than two times the prescribed wall thickness of the cylindrical shell. The cylinder end contour must be hemispherical or ellipsoidal with a ratio of major-to-minor axis not exceeding two to one and with the concave side to pressure.
(e) Welding or brazing. Welding or brazing for any purpose whatsoever is prohibited, except that welding by spinning is permitted to close the bottom of spun cylinders. Machining or grinding to produce proper surface finish at point of closure is required.
(f) Wall thickness. (1) Minimum wall thickness for any cylinder must be 0.050 inch. The minimum wall thickness must be such that the wall stress at the minimum specified test pressure may not exceed 75 percent of the minimum tensile strength of the steel as determined from the physical tests required in paragraph (m) of this section and may not be over 105,000 psi.
(2) Calculations must be made by the formula:
(3) Wall thickness of hemispherical bottoms only permitted to 90 percent of minimum wall thickness of cylinder sidewall but may not be less than 0.050 inch. In all other cases, thickness to be no less than prescribed minimum wall.
(g) Heat treatment. The completed cylinders must be uniformly and properly heated prior to tests. Heat treatment of the cylinders of the authorized analysis must be as follows:
(1) All cylinders must be quenched by oil, or other suitable medium.
(2) The steel temperature on quenching must be that recommended for the steel analysis, but may not exceed 1750 °F.
(3) The steel must be tempered at a temperature most suitable for the particular steel analysis but not less than 850 °F.
(4) All cylinders must be inspected by the magnetic particle or dye penetrant method to detect the presence of quenching cracks. Any cylinder found to have a quenching crack must be rejected and may not be requalified.
(h) Openings in cylinders and connections (valves, fuse plugs, etc.) for those openings. Threads conforming to the following are required on openings:
(1) Threads must be clean cut, even, without cracks, and to gauge.
(2) Taper threads, when used, must be of length not less than as specified for National Gas Tapered Thread (NGT) as required by American Standard Compressed Gas Cylinder Valve Outlet and Inlet Connections.
(3) Straight threads having at least 6 engaged threads are authorized. Straight threads must have a tight fit and a calculated shear stress of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to minimum of 5/3 times service pressure.
(3) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(j) Cycling tests. Prior to the initial shipment of any specific cylinder design, cyclic pressurization tests must have been performed on at least three representative samples without failure as follows:
(1) Pressurization must be performed hydrostatically between approximately zero psig and the service pressure at a rate not in excess of 10 cycles per minute. Adequate recording instrumentation must be provided if equipment is to be left unattended for periods of time.
(2) Tests prescribed in paragraph (j)(1) of this section must be repeated on one random sample out of each lot of cylinders. The cylinder may then be subjected to a burst test.
(3) A lot is defined as a group of cylinders fabricated from the same heat of steel, manufactured by the same process and heat treated in the same equipment under the same conditions of time, temperature, and atmosphere, and may not exceed a quantity of 200 cylinders.
(4) All cylinders used in cycling tests must be destroyed.
(k) Burst test. One cylinder taken at random out of each lot of cylinders must be hydrostatically tested to destruction.
(l) Flattening test. A flattening test must be performed on one cylinder taken at random out of each lot of 200 or less, by placing the cylinder between wedge shaped knife edges having a 60° included angle, rounded to 1/2 -inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to knife edges during the test. For lots of 30 or less, flattening tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to same heat treatment as the finished cylinder.
(m) Physical tests. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material, as follows:
(1) Test is required on 2 specimens cut from 1 cylinder taken at random out of each lot of cylinders.
(2) Specimens must conform to the following:
(i) A gauge length of at least 24 times the thickness with a width not over six times the thickness. The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section. When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with the record of physical tests detailed information in regard to such specimens.
(ii) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length.
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi, the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(n) Magnetic particle inspection. Inspection must be performed on the inside of each container before closing and externally on each finished container after heat treatment. Evidence of discontinuities, which in the opinion of a qualified inspector may appreciably weaken or decrease the durability of the cylinder, must be cause for rejection.
(o) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by dry gas or dry air pressure after the bottom has been cleaned and is free from all moisture, subject to the following conditions and limitations:
(1) Pressure, approximately the same as but not less than service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least one minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Except as provided in paragraph (q) of this section, a cylinder must be rejected if there is leakage.
(2) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(3) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(4) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, the manufacturer should design the test apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(p) Acceptable results of tests. Results of the flattening test, physical tests, burst test, and cycling test must conform to the following:
(1) Flattening required without cracking to ten times the wall thickness of the cylinder.
(2) Physical tests:
(i) An elongation of at least 6 percent for a gauge length of 24 times the wall thickness.
(ii) The tensile strength may not exceed 165,000 p.s.i.
(3) The burst pressure must be at least 4/3 times the test pressure.
(4) Cycling-at least 10,000 pressurizations.
(q) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair by welding or spinning is not authorized. For each cylinder subjected to reheat treatment during original manufacture, sidewall measurements must be made to verify that the minimum sidewall thickness meets specification requirements after the final heat treatment.
(r) Marking. (1) Cylinders must be marked by low stress type steel stamping in an area and to a depth which will insure that the wall thickness measured from the root of the stamping to the interior surface is equal to or greater than the minimum prescribed wall thickness. Stamping must be permanent and legible. Stamping on side wall not authorized.
(2) The rejection elastic expansion (REE), in cubic cm (cc), must be marked on the cylinder near the date of test. The REE for a cylinder is 1.05 times its original elastic expansion.
(3) Name plates are authorized, provided that they can be permanently and securely attached to the cylinder. Attachment by either brazing or welding is not permitted. Attachment by soldering is permitted provided steel temperature does not exceed 500 °F.
(s) Inspector's report. In addition to the requirements of § 178.35, the inspector's report must indicate the rejection elastic expansion (REE), in cubic cm (cc).
§ 178.45   Specification 3T seamless steel cylinder.
(a) Type, size, and service pressure. A DOT 3T cylinder is a seamless steel cylinder with a minimum water capacity of 1,000 pounds and a minimum service pressure of 1,800 psig. Each cylinder must have integrally formed heads concave to pressure at both ends. The inside head shape must be hemispherical, ellipsoidal in which the major axis is two times the minor axis, or a dished shape falling within these two limits. Permanent closures formed by spinning are prohibited.
(b) Material, steel. Only open hearth, basic oxygen, or electric furnace process steel of uniform quality is authorized. The steel analysis must conform to the following:
Analysis Tolerances
(1) A heat of steel made under the specifications in the table in this paragraph (b), the ladle analysis of which is slightly out of the specified range, is acceptable if satisfactory in all other aspects. However, the check analysis tolerances shown in the table in this paragraph (b) may not be exceeded except as approved by the Department.
(2) Material with seams, cracks, laminations, or other injurious defects is not permitted.
(3) Material used must be identified by any suitable method.
(c) Manufacture. General manufacturing requirements are as follows:
(1) Surface finish must be uniform and reasonably smooth.
(2) Inside surfaces must be clean, dry, and free of loose particles.
(3) No defect of any kind is permitted if it is likely to weaken a finished cylinder.
(4) If the cylinder surface is not originally free from the defects, the surface may be machined or otherwise treated to eliminate these defects provided the minimum wall thickness is maintained.
(5) Welding or brazing on a cylinder is not permitted.
(d) Wall thickness. The minimum wall thickness must be such that the wall stress at the minimum specified test pressure does not exceed 67 percent of the minimum tensile strength of the steel as determined by the physical tests required in paragraphs (j) and (k) of this section. A wall stress of more than 90,500 p.s.i. is not permitted. The minimum wall thickness for any cylinder may not be less than 0.225 inch.
(1) Calculation of the stress for cylinders must be made by the following formula:
(2) Each cylinder must meet the following additional requirement which assumes a cylinder horizontally supported at its two ends and uniformly loaded over its entire length. This load consists of the weight per inch of length of the straight cylindrical portion filled with water compressed to the specified test pressure. The wall thickness must be increased when necessary to meet this additional requirement:
(i) The sum of two times the maximum tensile stress in the bottom fibers due to bending (see paragraph (d)(2)(ii) of this section), plus the maximum tensile stress in the same fibers due to hydrostatic testing (see paragraph (d)(2)(iii) of this section) may not exceed 80 percent of the minimum yield strength of the steel at this maximum stress.
(ii) The following formula must be used to calculate the maximum tensile stress due to bending:
(iii) The following formula must be used to calculate the maximum longitudinal tensile stress due to hydrostatic test pressure:
(e) Heat treatment. Each completed cylinder must be uniformly and properly heat treated prior to testing, as follows:
(1) Each cylinder must be heated and held at the proper temperature for at least one hour per inch of thickness based on the maximum thickness of the cylinder and then quenched in a suitable liquid medium having a cooling rate not in excess of 80 percent of water. The steel temperature on quenching must be that recommended for the steel analysis, but it must never exceed 1750 °F.
(2) After quenching, each cylinder must be reheated to a temperature below the transformation range but not less than 1050 °F., and must be held at this temperature for at least one hour per inch of thickness based on the maximum thickness of the cylinder. Each cylinder must then be cooled under conditions recommended for the steel.
(f) Openings. Openings in cylinders must comply with the following:
(1) Openings are permitted on heads only.
(2) The size of any centered opening in a head may not exceed one half the outside diameter of the cylinder.
(3) Openings in a head must have ligaments between openings of at least three times the average of their hole diameter. No off-center opening may exceed 2.625 inches in diameter.
(4) All openings must be circular.
(5) All openings must be threaded. Threads must be in compliance with the following:
(i) Each thread must be clean cut, even, without any checks, and to gauge.
(ii) Taper threads, when used, must be the American Standard Pipe thread (NPT) type and must be in compliance with the requirements of NBS Handbook H-28 (IBR, see § 171.7 of this subchapter).
(iii) Taper threads conforming to National Gas Taper thread (NGT) standards must be in compliance with the requirements of NBS Handbook H-28.
(iv) Straight threads conforming with National Gas Straight thread (NGS) standards are authorized. These threads must be in compliance with the requirements of NBS Handbook H-28.
(g) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to minimum of 5/3 times service pressure.
(3) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(h) Ultrasonic examination. After the hydrostatic test, the cylindrical section of each vessel must be examined in accordance with ASTM E 213 for shear wave and E 114 for straight beam (IBR, Standard see § 171.7 of this subchapter). The equipment used must be calibrated to detect a notch equal to five percent of the design minimum wall thickness. Any discontinuity indication greater than that produced by the five percent notch must be cause for rejection of the cylinder, unless the discontinuity is repaired within the requirements of this specification.
(i) Basic requirements for tension and Charpy impact tests. Cylinders must be subjected to a tension and Charpy impact as follows:
(1) When the cylinders are heat treated in a batch furnace, two tension specimens and three Charpy impact specimens must be tested from one of the cylinders or a test ring from each batch. The lot size represented by these tests may not exceed 200 cylinders.
(2) When the cylinders are heat treated in a continuous furnace, two tension specimens and three Charpy impact specimens must be tested from one of the cylinders or a test ring from each four hours or less of production. However, in no case may a test lot based on this production period exceed 200 cylinders.
(3) Each specimen for the tension and Charpy impact tests must be taken from the side wall of a cylinder or from a ring which has been heat treated with the finished cylinders of which the specimens must be representative. The axis of the specimens must be parallel to the axis of the cylinder. Each cylinder or ring specimen for test must be of the same diameter, thickness, and metal as the finished cylinders they represent. A test ring must be at least 24 inches long with ends covered during the heat treatment process so as to simulate the heat treatment process of the finished cylinders it represents.
(4) A test cylinder or test ring need represent only one of the heats in a furnace batch provided the other heats in the batch have previously been tested and have passed the tests and that such tests do not represent more than 200 cylinders from any one heat.
(5) The test results must conform to the requirements specified in paragraphs (j) and (k) of this section.
(6) When the test results do not conform to the requirements specified, the cylinders represented by the tests may be reheat treated and the tests repeated. Paragraph (i)(5) of this section applies to any retesting.
(j) Basic conditions for acceptable physical testing. The following criteria must be followed to obtain acceptable physical test results:
(1) Each tension specimen must have a gauge length of two inches with a width not exceeding one and one-half inches. Except for the grip ends, the specimen may not be flattened. The grip ends may be flattened to within one inch of each end of the reduced section.
(2) A specimen may not be heated after heat treatment specified in paragraph (d) of this section.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gage length.
(i) This yield strength must be determined by the “offset” method or the “extension under load” method described in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) For the “extension under load” method, the total strain (or extension under load) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gage length under appropriate load and adding thereto 0.2 percent of the gage length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. However, when the degree of accuracy of this method is questionable the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set with the specimen under a stress of 12,000 p.s.i. and the strain indicator reading set at the calculated corresponding strain.
(iv) The cross-head speed of the testing machine may not exceed 1/8 inch per minute during the determination of yield strength.
(4) Each impact specimen must be Charpy V-notch type size 10 mm × 10 mm taken in accordance with paragraph 11 of ASTM A 333 (IBR, see § 171.7 of this subchapter). When a reduced size specimen is used, it must be the largest size obtainable.
(k) Acceptable physical test results. Results of physical tests must conform to the following:
(1) The tensile strength may not exceed 155,000 p.s.i.
(2) The elongation must be at least 16 percent for a two-inch gage length.
(3) The Charpy V-notch impact properties for the three impact specimens which must be tested at 0 °F may not be less than the values shown as follows:
(4) After the final heat treatment, each vessel must be hardness tested on the cylindrical section. The tensile strength equivalent of the hardness number obtained may not be more than 165,000 p.s.i. (Rc 36). When the result of a hardness test exceeds the maximum permitted, two or more retests may be made; however, the hardness number obtained in each retest may not exceed the maximum permitted.
(l) Rejected cylinders. Reheat treatment is authorized for rejected cylinders. However, each reheat treated cylinder must subsequently pass all the prescribed tests. Repair by welding is not authorized.
(m) Markings. Marking must be done by stamping into the metal of the cylinder. All markings must be legible and located on a shoulder.
(n) Inspector's report. In addition to the requirements of § 178.35, the inspector's report for the physical test report, must indicate the average value for three specimens and the minimum value for one specimen for each lot number.
§ 178.46   Specification 3AL seamless aluminum cylinders.
(a) Size and service pressure. A DOT 3AL cylinder is a seamless aluminum cylinder with a maximum water capacity of 1000 pounds and minimum service pressure of 150 psig.
(b) Authorized material and identification of material. The material of construction must meet the following conditions:
(1) Starting stock must be cast stock or traceable to cast stock.
(2) Material with seams, cracks, laminations, or other defects likely to weaken the finished cylinder may not be used.
(3) Material must be identified by a suitable method that will identify the alloy, the aluminum producer's cast number, the solution heat treat batch number and the lot number.
(4) The material must be of uniform quality. Only the following heat treatable aluminum alloys in table 1 and 2 are permitted as follows:
Table 1—Heat or Cast Analysis for Aluminum; Similar to “Aluminum Association” 1 Alloy 6061
[CHEMICAL ANALYSIS IN WEIGHT PERCENT 2 ]
1 The “Aluminum Association” refers to “Aluminum Standards and Data 1993”, published by the Aluminum Association Inc.
2 Except for “Pb” and “Bi”, the chemical composition corresponds with that of Table 1 of ASTM B 221 (IBR, see § 171.7 of this subchapter) for Aluminum Association alloy 6061.
Table 2—Mechanical Property Limits
1 “D” represents specimen diameters. When the cylinder wall is greater than 3/16 inch thick, a retest without reheat treatment using the 4D size specimen is authorized if the test using the 2 inch size specimen fails to meet elongation requirements.
2 When cylinder wall is not over 3/16 -inch thick, 10 percent elongation is authorized when using a 24t × 6t size test specimen.
(5) All starting stock must be 100 percent ultrasonically inspected, along the length at right angles to the central axis from two positions at 90° to one another. The equipment and continuous scanning procedure must be capable of detecting and rejecting internal defects such as cracks which have an ultrasonic response greater than that of a calibration block with a 5/64 -inch diameter flat bottomed hole.
(6) Cast stock must have uniform equiaxed grain structure not to exceed 500 microns maximum.
(7) Any starting stock not complying with the provisions of paragraphs (b)(1) through (b)(6) of this section must be rejected.
(c) Manufacture. Cylinders must be manufactured in accordance with the following requirements:
(1) Cylinder shells must be manufactured by the backward extrusion method and have a cleanliness level adequate to ensure proper inspection. No fissure or other defect is acceptable that is likely to weaken the finished cylinder below the design strength requirements. A reasonably smooth and uniform surface finish is required. If not originally free from such defects, the surface may be machined or otherwise conditioned to eliminate these defects.
(2) Thickness of the cylinder base may not be less than the prescribed minimum wall thickness of the cylindrical shell. The cylinder base must have a basic torispherical, hemispherical, or ellipsoidal interior base configuration where the dish radius is no greater than 1.2 times the inside diameter of the shell. The knuckle radius may not be less than 12 percent of the inside diameter of the shell. The interior base contour may deviate from the true torispherical, hemispherical or ellipsoidal configuration provided that—
(i) Any areas of deviation are accompanied by an increase in base thickness;
(ii) All radii of merging surfaces are equal to or greater than the knuckle radius;
(iii) Each design has been qualified by successfully passing the cycling tests in this paragraph (c); and
(iv) Detailed specifications of the base design are available to the inspector.
(3) For free standing cylinders, the base thickness must be at least two times the minimum wall thickness along the line of contact between the cylinder base and the floor when the cylinders are in the vertical position.
(4) Welding or brazing is prohibited.
(5) Each new design and any significant change to any acceptable design must be qualified for production by testing prototype samples as follows:
(i) Three samples must be subjected to 100,000 pressure reversal cycles between zero and service pressure or 10,000 pressure reversal cycles between zero and test pressure, at a rate not in excess of 10 cycles per minute without failure.
(ii) Three samples must be pressurized to destruction and failure may not occur at less than 2.5 times the marked cylinder service pressure. Each cylinder must remain in one piece. Failure must initiate in the cylinder sidewall in a longitudinal direction. Rate of pressurization may not exceed 200 psig per second.
(6) In this specification “significant change” means a 10 percent or greater change in cylinder wall thickness, service pressure, or diameter; a 30 percent or greater change in water capacity or base thickness; any change in material; over 100 percent increase in size of openings; or any change in the number of openings.
(d) Wall thickness. The minimum wall thickness must be such that the wall stress at the minimum specified test pressure will not exceed 80 percent of the minimum yield strength nor exceed 67 percent of the minimum ultimate tensile strength as verified by physical tests in paragraph (i) of this section. The minimum wall thickness for any cylinder with an outside diameter greater than 5 inches must be 0.125 inch. Calculations must be made by the following formula:
(e) Openings. Openings must comply with the following requirements:
(1) Openings are permitted in heads only.
(2) The size of any centered opening in a head may not exceed one-half the outside diameter of the cylinder.
(3) Other openings are permitted in the head of a cylinder if:
(i) Each opening does not exceed 2.625 inches in diameter, or one-half the outside diameter of the cylinder; whichever is less;
(ii) Each opening is separated from each other by a ligament; and
(iii) Each ligament which separates two openings must be at least three times the average of the diameters of the two openings.
(4) All openings must be circular.
(5) All openings must be threaded. Threads must comply with the following:
(i) Each thread must be clean cut, even, without checks, and to gauge.
(ii) Taper threads, when used, must conform to one of the following:
(A) American Standard Pipe Thread (NPT) type, conforming to the requirements of NBS Handbook H-28 (IBR, see § 171.7 of this subchapter);
(B) National Gas Taper Thread (NGT) type, conforming to the requirements of NBS Handbook H-28; or
(C) Other taper threads conforming to other standards may be used provided the length is not less than that specified for NPT threads.
(iii) Straight threads, when used, must conform to one of the following:
(A) National Gas Straight Thread (NGS) type, conforming to the requirements of NBS Handbook H-28;
(B) Unified Thread (UN) type, conforming to the requirements of NBS Handbook H-28;
(C) Controlled Radius Root Thread (UN) type, conforming to the requirements of NBS Handbook H-28; or
(D) Other straight threads conforming to other recognized standards may be used provided that the requirements in paragraph (e)(5)(iv) of this section are met.
(iv) All straight threads must have at least 6 engaged threads, a tight fit, and a factor of safety in shear of at least 10 at the test pressure of the cylinder. Shear stress must be calculated by using the appropriate thread shear area in accordance with NBS Handbook H-28.
(f) Heat treatment. Prior to any test, all cylinders must be subjected to a solution heat treatment and aging treatment appropriate for the aluminum alloy used.
(g) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) The minimum test pressure must be the greater of the following:
(i) 450 psig regardless of service pressure;
(ii) Two (2) times the service pressure for cylinders having service pressure less than 500 psig; or
(iii) 5/3 times the service pressure for cylinders having a service pressure of 500 psig or greater.
(3) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2, however, if a second failure to maintain the test pressure occurs the cylinder being tested must be rejected.
(4) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(h) Flattening test. One cylinder taken at random out of each lot must be subjected to a flattening test as follows:
(1) The test must be between knife edges, wedge shaped, having a 60° included angle, and rounded in accordance with the following table. The longitudinal axis of the cylinder must be at an angle 90° to the knife edges during the test. The flattening test table is as follows:
Table 3—Flattening Test Table
(2) An alternate bend test in accordance with ASTM E 290 using a mandrel diameter not more than 6 times the wall thickness is authorized to qualify lots that fail the flattening test of this section without reheat treatment. If used, this test must be performed on two samples from one cylinder taken at random out of each lot of 200 cylinders or less.
(3) Each test cylinder must withstand flattening to nine times the wall thickness without cracking. When the alternate bend test is used, the test specimens must remain uncracked when bent inward around a mandrel in the direction of curvature of the cylinder wall until the interior edges are at a distance apart not greater than the diameter of the mandrel.
(i) Mechanical properties test. Two test specimens cut from one cylinder representing each lot of 200 cylinders or less must be subjected to the mechanical properties test, as follows:
(1) The results of the test must conform to at least the minimum acceptable mechanical property limits for aluminum alloys as specified in paragraph (b) of this section.
(2) Specimens must be 4D bar or gauge length 2 inches with width not over 1 1/2 inch taken in the direction of extrusion approximately 180° from each other; provided that gauge length at least 24 times thickness with width not over 6 times thickness is authorized, when cylinder wall is not over 3/16 inch thick. The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section. When the size of the cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold by pressure only, not by blows. When such specimens are used, the inspector's report must show that the specimens were so taken and prepared. Heating of specimens for any purpose is forbidden.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length.
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM B 557 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 10,000,000 psi. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 6,000 psi, the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(j) Rejected cylinder. Reheat treatment of rejected cylinders is authorized one time. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable.
(k) Duties of inspector. In addition to the requirements of § 178.35, the inspector shall:
(1) Verify compliance with the provisions of paragraph (b) of this section by:
(i) Performing or witnessing the performance of the chemical analyses on each melt or cast lot or other unit of starting material; or
(ii) Obtaining a certified chemical analysis from the material or cylinder manufacturer for each melt, or cast of material; or
(iii) Obtaining a certified check analysis on one cylinder out of each lot of 200 cylinders or less, if a certificate containing data to indicate compliance with the material specification is obtained.
(2) The inspector must verify ultrasonic inspection of all material by inspection or by obtaining the material producer's certificate of ultrasonic inspection. Ultrasonic inspection must be performed or verified as having been performed in accordance with paragraph (b)(5) of this section.
(3) The inspector must also determine that each cylinder complies with this specification by:
(i) Selecting the samples for check analyses performed by other than the material producer;
(ii) Verifying that the prescribed minimum thickness was met by measuring or witnessing the measurement of the wall thickness; and
(iii) Verifying that the identification of material is proper.
(4) Prior to initial production of any design or design change, verify that the design qualification tests prescribed in paragraph (c)(6) of this section have been performed with acceptable results.
(l) Definitions. (1) In this specification, a “lot” means a group of cylinders successively produced having the same:
(i) Size and configuration;
(ii) Specified material of construction;
(iii) Process of manufacture and heat treatment;
(iv) Equipment of manufacture and heat treatment; and
(v) Conditions of time, temperature and atmosphere during heat treatment.
(2) In no case may the lot size exceed 200 cylinders, but any cylinder processed for use in the required destructive physical testing need not be counted as being one of the 200.
(m) Inspector's report. In addition to the information required by § 178.35, the record of chemical analyses must also include the alloy designation, and applicable information on iron, titanium, zinc, magnesium and any other applicable element used in the construction of the cylinder.
§ 178.47   Specification 4DS welded stainless steel cylinders for aircraft use.
(a) Type, size, and service pressure. A DOT 4DS cylinder is either a welded stainless steel sphere (two seamless hemispheres) or circumferentially welded cylinder both with a water capacity of not over 100 pounds and a service pressure of at least 500 but not over 900 psig.
(b) Steel. Types 304, 321 and 347 stainless steel are authorized with proper welding procedure. A heat of steel made under the specifications in table 1 in this paragraph (b), check chemical analysis of which is slightly out of the specified range, is acceptable, if satisfactory in all other respects, provided the tolerances shown in table 2 in this paragraph (b) are not exceeded, except as approved by Associate Administrator. The following chemical analyses are authorized:
Table 1—Authorized Materials
1 Titanium may not be more than 5C and not more than 0.60%.
2 Columbium may not be less than 10C and not more than 1.0%.
Table 2—Check Analysis Tolerances
1 Rephosphorized steels not subject to check analysis for phosphorus.
(c) Identification of material. Materials must be identified by any suitable method.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably, a reasonably smooth and uniform surface finish is required. No abrupt change in wall thickness is permitted. Welding procedures and operators must be qualified in accordance with CGA Pamphlet C-3 (IBR, see § 171.7 of this subchapter). All seams of the sphere or cylinder must be fusion welded. Seams must be of the butt type and means must be provided for accomplishing complete penetration of the joint.
(e) Attachments. Attachments to the container are authorized by fusion welding provided that such attachments are made of weldable stainless steel in accordance with paragraph (b) of this section.
(f) Wall thickness. The minimum wall thickness must be such that the wall stress at the minimum specified test pressure may not be over 60,000 psig. A minimum wall thickness of 0.040 inch is required for any diameter container. Calculations must be made by the following formulas:
(1) Calculation for sphere must be made by the formula:
(2) Calculation for a cylinder must be made by the formula:
(g) Heat treatment. The seamless hemispheres and cylinders may be stress relieved or annealed for forming. Welded container must be stress relieved at a temperature of 775 °F ±25° after process treatment and before hydrostatic test.
(h) Openings in container. Openings must comply with the following:
(1) Each opening in the container must be provided with a fitting, boss or pad of weldable stainless steel securely attached to the container by fusion welding.
(2) Attachments to a fitting, boss, or pad must be adequate to prevent leakage. Threads must comply with the following:
(i) Threads must be clean cut, even, without checks, and tapped to gauge.
(ii) Taper threads to be of length not less than as specified for American Standard taper pipe threads.
(iii) Straight threads having at least 4 engaged threads, to have tight fit and calculated shear strength at least 10 times the test pressure of the container; gaskets required, adequate to prevent leakage.
(i) Process treatment. Each container must be hydraulically pressurized in a water jacket to at least 100 percent, but not more than 110 percent, of the test pressure and maintained at this pressure for a minimum of 3 minutes. Total and permanent expansion must be recorded and included in the inspector's report.
(j) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) The test must be by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(2) Each cylinder must be tested to a minimum of at least two (2) times its service pressure.
(3) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(4) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(5) The cylinder must then be inspected. Any wall thickness lower than that required by paragraph (f) of this section must be cause for rejection. Bulges and cracks must be cause for rejection. Welded joint defects exceeding requirements of paragraph (k) of this section are cause for rejection.
(k) Radiographic inspection. Radiographic inspection is required on all welded joints which are subjected to internal pressure, except that at the discretion of the disinterested inspector, openings less than 25 percent of the container diameter need not be subjected to radiographic inspection. Evidence of any defects likely to seriously weaken the container is cause for rejection. Radiographic inspection must be performed subsequent to the hydrostatic test.
(l) Burst test. One container taken at random out of 200 or less must be hydrostatically tested to destruction. Rupture pressure must be included as part of the inspector's report.
(m) Flattening test. A flattening test must be performed as follows:
(1) For spheres the test must be at the weld between parallel steel plates on a press with welded seam at right angles to the plates. Test one sphere taken at random out of each lot of 200 or less after the hydrostatic test. Any projecting appurtenances may be cut off (by mechanical means only) prior to crushing.
(2) For cylinders the test must be between knife edges, wedge shaped, 60° angle, rounded to 1/2 -inch radius. Test one cylinder taken at random out of each lot of 200 or less, after the hydrostatic test.
(n) Acceptable results for flattening and burst tests. Acceptable results for flattening and burst tests are as follows:
(1) Flattening required to 50 percent of the original outside diameter without cracking.
(2) Burst pressure must be at least 3 times the service pressure.
(o) Rejected containers. Repair of welded seams by welding prior to process treatment is authorized. Subsequent thereto, containers must be heat treated and pass all prescribed tests.
(p) Duties of inspector. In addition to the requirements of § 178.35, the inspector must verify that all tests are conducted at temperatures between 60 °F and 90 °F.
(q) Marking. Markings must be stamped plainly and permanently on a permanent attachment or on a metal nameplate permanently secured to the container by means other than soft solder.
§ 178.50   Specification 4B welded or brazed steel cylinders.
(a) Type, size, pressure, and application. A DOT 4B is a welded or brazed steel cylinder with water capacity (nominal) not over 1,000 pounds and a service pressure of at least 150 but not over 500 psig. Longitudinal seams must be forged lap-welded or brazed. Cylinders closed in by spinning process are not authorized.
(b) Steel. Open-hearth, electric or basic oxygen process steel of uniform quality must be used. Content percent may not exceed the following: Carbon, 0.25; phosphorus, 0.045; sulphur, 0.050. The cylinder manufacturer must maintain a record of intentionally added alloying elements.
(c) Identification of material. Pressure-retaining materials must be identified by any suitable method that does not compromise the integrity of the cylinder. Plates and billets for hotdrawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. Exposed bottom welds on cylinders over 18 inches long must be protected by footrings. Welding procedures and operators must be qualified in conformance with CGA C-3 (IBR, see § 171.7 of this subchapter). Seams must be made as follows:
(1) Brazing materials. Brazing materials must be by copper brazing, by copper alloy brazing, or by silver alloy brazing. Copper alloy composition must be: Copper, 95 percent minimum; Silicon, 1.5 percent to 3.85 percent; Manganese, 0.25 percent to 1.10 percent.
(2) Brazed circumferential seams. Heads attached by brazing must have a driving fit with the shell, unless the shell is crimped, swedged, or curled over the skirt or flange of the head, and be thoroughly brazed until complete penetration by the brazing material of the brazed joint is secured. Depth of brazing of the joint must be at least four (4) times the minimum thickness of shell metal.
(3) Welded circumferential seams. Circumferential seams are permitted by the welding process.
(4) Longitudinal seams in shells. Longitudinal seams must be a forged lap joint design. When brazed, the plate edge must be lapped at least eight (8) times the thickness of the plate, laps being held in position, substantially metal to metal, by riveting or electric spot-welding; brazing must be done by using a suitable flux and by placing brazing material on one side of seam and applying heat until this material shows uniformly along the seam of the other side.
(e) Welding or brazing. Only the attachment of neckrings, footrings, handles, bosses, pads, and valve protection rings to the tops and bottoms of cylinders by welding or brazing is authorized. Attachments and the portion of the cylinder to which they are attached must be made of weldable steel, the carbon content of which may not exceed 0.25 percent except in the case of 4130X steel, which may be used with proper welding procedure.
(f) Wall thickness. The wall thickness of the cylinder must comply with the following requirements:
(1) For cylinders with outside diameters over 6 inches, the minimum wall thickness must be 0.090 inch. In any case, the minimum wall thickness must be such that calculated wall stress at minimum test pressure (paragraph (i)(4) of this section) may not exceed the following values:
(i) 24,000 psig for cylinders without longitudinal seam.
(ii) 22,800 psig for cylinders having copper brazed or silver alloy brazed longitudinal seam.
(iii) 18,000 psig for cylinders having forged lapped welded longitudinal seam.
(2) Calculation must be made by the formula:
(g) Heat treatment. Cylinder heads, bodies or the completed cylinder, formed by drawing or pressing, must be uniformly and properly heat treated by an applicable method shown in table 1 of appendix A of this part before tests.
(h) Opening in cylinders. Openings in cylinders must comply with the following:
(1) Any opening must be placed on other than a cylindrical surface.
(2) Each opening in a spherical type of cylinder must be provided with a fitting, boss, or pad of weldable steel securely attached to the cylinder by fusion welding.
(3) Each opening in a cylindrical type cylinder, except those for pressure relief devices, must be provided with a fitting, boss, or pad, securely attached to container by brazing or by welding.
(4) If threads are used, they must comply with the following:
(i) Threads must be clean cut, even without checks, and tapped to gauge.
(ii) Taper threads must be of a length not less than as specified for American Standard taper pipe threads.
(iii) Straight threads, must have at least four (4) engaged threads, must have tight fit and a calculated shear strength at least ten (10) times the test pressure of the cylinder; gaskets are required for straight threads and must be of sufficient quality to prevent leakage.
(iv) A brass fitting may be brazed to the steel boss or flange on cylinders used as component parts of handheld fire extinguishers.
(5) The closure of a fitting, boss, or pad must be adequate to prevent leakage.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows: (1) Lot testing. (i) At least one (1) cylinder randomly selected out of each lot of 200 or fewer must be tested by the water jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of 2 times service pressure.
(iii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(2) Pressure testing. (i) The remaining cylinders in the lot must be tested by the proof pressure, water-jacket, or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. Further, all testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, sections 5.7.2 or 7.1.2, as appropriate. Determination of expansion properties is not required.
(ii) Each cylinder must be tested to a minimum of at least two (2) times service pressure and show no defect.
(j) Mechanical test. A mechanical test must be conducted to determine yield strength, tensile strength, elongation as a percentage, and reduction of area of material as a percentage as follows:
(1) Testing is required on two (2) specimens removed from one (1) cylinder, or part thereof, heat-treated as required, as illustrated in appendix A to this subpart. For lots of 30 or fewer, mechanical tests are authorized to be made on a ring at least 8 inches long removed from each cylinder and subjected to the same heat treatment as the finished cylinder.
(2) Specimens must comply with the following:
(i) When a cylinder wall is 3/16 inch thick or less, one the following gauge lengths is authorized: A gauge length of 8 inches with a width not over 1 1/2 inches, a gauge length of 2 inches with a width not over 1 1/2 inches, or a gauge length at least twenty-four (24) times the thickness with a width not over six (6) times the thickness.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When the size of a cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are taken and prepared using this method, the inspector's report must show detailed information regarding such specimens in connection with the record of mechanical tests.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For strain measurement, the initial strain reference must be set while the specimen is under a stress of 12,000 psig, and strain indicator reading must be set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(v) The yield strength must not exceed 73 percent of the tensile strength.
(k) Elongation. Mechanical test specimens must show at least a 40 percent elongation for a 2-inch gauge length or at least 20 percent in other cases. However, elongation percentages may be reduced numerically by 2 percent for 2-inch specimens, and by 1 percent in other cases, for each 7,500 psig increase of tensile strength above 50,000 psig. The tensile strength may be incrementally increased by four increments of 7,500 psig for a maximum total of 30,000 psig.
(l) Flattening test —(1) Cylinders. After pressure testing, a flattening test must be performed on one cylinder taken at random out of each lot of 200 or fewer by placing the cylinder between wedge-shaped knife edges having a 60 degree included angle, rounded to a half-inch radius. The longitudinal axis of the cylinder must be at a 90-degree angle to knife edges during the test. For lots of 30 or fewer, flattening tests are authorized to be performed on a ring of at least 8 inches long removed from each cylinder and subjected to the same heat treatment as the finished cylinder.
(2) Pipes. When cylinders are constructed of lap welded pipe, an additional flattening test is required, without evidence of cracking, up to six (6) times the wall thickness. In such case, the rings (crop ends) removed from each end of the pipe, must be tested with the weld 45 °F or less from the point of greatest stress.
(m) Acceptable results for flattening tests. There must be no evidence of cracking of the sample when it is flattened between flat plates to no more than six (6) times the wall thickness. If this test fails, one additional sample from the same lot may be taken. If this second sample fails, the entire lot must be rejected.
(n) Rejected cylinders. Reheat treatment is authorized for a rejected cylinder in accordance with this paragraph (n). After reheat treatment, a cylinder must pass all prescribed tests in this section to be considered acceptable. Repair of brazed seams by brazing and welded seams by welding is authorized. For cylinders with an outside diameter of less than or equal to six (6) inches, welded seam repairs greater than one (1) inch in length shall require reheat treatment of the cylinder. For cylinders greater than an outside diameter of 6 inches, welded seam repairs greater than three (3) inches in length shall require reheat treatment.
(o) Markings. (1) Markings must be as required as in § 178.35 and in addition must be stamped plainly and permanently in any of the following locations on the cylinder:
(i) On shoulders and top heads whose wall thickness is not less than 0.087-inch thick;
(ii) On side wall adjacent to top head for side walls which are not less than 0.090 inch thick;
(iii) On a cylindrical portion of the shell that extends beyond the recessed bottom of the cylinder, constituting an integral and non-pressure part of the cylinder;
(iv) On a metal plate attached to the top of the cylinder or permanent part thereof; sufficient space must be left on the plate to provide for stamping at least six retest dates; the plate must be at least 1/16 -inch thick and must be attached by welding, or by brazing. The brazing rod must melt at a temperature of 1100 °F. Welding or brazing must be along all the edges of the plate;
(v) On the neck, neckring, valve boss, valve protection sleeve, or similar part permanently attached to the top of the cylinder; or
(vi) On the footring permanently attached to the cylinder, provided the water capacity of the cylinder does not exceed 30 pounds.
(2) Embossing the cylinder head or sidewall is not permitted.
§ 178.51   Specification 4BA welded or brazed steel cylinders.
(a) Type, size, pressure, and application. A DOT 4BA cylinder is a cylinder, either spherical or cylindrical design, with a water capacity of 1,000 pounds or less and a service pressure range of 225 to 500 psig. Closures made by the spinning process are not authorized.
(1) Spherical type cylinder designs are permitted to have only one circumferentially welded seam.
(2) Cylindrical type cylinder designs must be of circumferentially welded or brazed construction; longitudinally brazed or silver-soldered seams are also permitted.
(b) Steel. The steel used in the construction of the cylinder must be as specified in table 1 of appendix A to this part. The cylinder manufacturer must maintain a record of intentionally added alloying elements.
(c) Identification of material. Pressure-retaining material must be identified by any suitable method that does not compromise the integrity of the cylinder. Plates and billets for hotdrawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. Exposed bottom welds on cylinders over 18 inches long must be protected by footrings.
(1) Seams must be made as follows:
(i) Minimum thickness of heads and bottoms must be not less than 90 percent of the required thickness of the side wall.
(ii) Circumferential seams must be made by welding or by brazing. Heads attached by brazing must have a driving fit with the shell unless the shell is crimped, swedged, or curled over the skirt or flange of the head and must be thoroughly brazed until complete penetration by the brazing material of the brazed joint is secured. Depth of brazing from end of the shell must be at least four (4) times the thickness of shell metal.
(iii) Longitudinal seams in shells must be made by copper brazing, copper alloy brazing, or by silver alloy brazing. Copper alloy composition must be: Copper 95 percent minimum, Silicon 1.5 percent to 3.85 percent, Manganese 0.25 percent to 1.10 percent. The melting point of the silver alloy brazing material must be in excess of 1,000 °F. The plate edge must be lapped at least eight times the thickness of plate, laps being held in position, substantially metal to metal, by riveting or by electric spot-welding. Brazing must be done by using a suitable flux and by placing brazing material on one side of seam and applying heat until this material shows uniformly along the seam of the other side. Strength of longitudinal seam: Copper brazed longitudinal seam must have strength at least 3/2 times the strength of the steel wall.
(2) Welding procedures and operators must be qualified in conformance with CGA C-3 (IBR, see § 171.7 of this subchapter).
(e) Welding or brazing. Welding or brazing of any attachment or opening to the heads of cylinders is permitted provided the carbon content of the steel does not exceed 0.25 percent except in the case of 4130 × steel, which may be used with proper welding procedure.
(f) Wall thickness. The minimum wall thickness of the cylinder must meet the following conditions:
(1) For any cylinder with an outside diameter of greater than 6 inches, the minimum wall thickness is 0.078 inch. In any case, the minimum wall thickness must be such that the calculated wall stress at the minimum test pressure may not exceed the lesser value of any of the following:
(i) The value shown in table 1 of appendix A to this part, for the material under consideration;
(ii) One-half of the minimum tensile strength of the material determined as required in paragraph (j) of this section;
(iii) 35,000 psig; or
(iv) Further provided that wall stress for cylinders having copper brazed longitudinal seams may not exceed 95 percent of any of the above values. Measured wall thickness may not include galvanizing or other protective coating.
(2) Cylinders that are cylindrical in shape must have the wall stress calculated by the formula:
(3) Cylinders that are spherical in shape must have the wall stress calculated by the formula:
(4) For a cylinder with a wall thickness less than 0.100 inch, the ratio of tangential length to outside diameter may not exceed 4.1.
(g) Heat treatment. Cylinders must be heat treated in accordance with the following requirements:
(1) Each cylinder must be uniformly and properly heat treated prior to test by the applicable method shown in table 1 of appendix A to this part. Heat treatment must be accomplished after all forming and welding operations, except that when brazed joints are used, heat treatment must follow any forming and welding operations, but may be done before, during or after the brazing operations (see paragraph (m) of this section for weld repairs).
(2) Heat treatment is not required after the welding or brazing of weldable low carbon parts to attachments of similar material which have been previously welded or brazed to the top or bottom of cylinders and properly heat treated, provided such subsequent welding or brazing does not produce a temperature in excess of 400 °F in any part of the top or bottom material.
(h) Openings in cylinders. Openings in cylinders must comply with the following requirements:
(1) Any opening must be placed on other than a cylindrical surface.
(2) Each opening in a spherical type cylinder must be provided with a fitting, boss, or pad of weldable steel securely attached to the container by fusion welding.
(3) Each opening in a cylindrical type cylinder must be provided with a fitting, boss, or pad, securely attached to container by brazing or by welding.
(4) If threads are used, they must comply with the following:
(i) Threads must be clean-cut, even, without checks and tapped to gauge.
(ii) Taper threads must be of a length not less than that specified for American Standard taper pipe threads.
(iii) Straight threads, having at least 4 engaged threads, must have a tight fit and a calculated shear strength of at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) Lot testing. (i) At least one (1) cylinder randomly selected out of each lot of 200 or fewer must be tested by water jacket or direct expansion method as prescribed in CGA C-1 (IBR, see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) The selected cylinder must be tested to a minimum of two (2) times service pressure.
(iii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(2) Pressure testing. (i) The remaining cylinders in the lot must be tested by the proof pressure, water-jacket, or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. Further, all testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure and show no defect. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2, as appropriate. Determination of expansion properties is not required.
(j) Mechanical test. (1) A mechanical test must be conducted to determine yield strength, tensile strength, elongation as a percentage, and reduction of area of material as a percentage, as follows:
(i) Cylinders. Testing is required on two (2) specimens removed from one cylinder or part thereof taken at random out of each lot of 200 or fewer. Samples must be removed after heat treatment as illustrated in appendix A to this subpart.
(ii) Spheres. Testing is required on two (2) specimens removed from the sphere or flat representative sample plates of the same heat of material taken at random from the steel used to produce the spheres. Samples (including plates) must be taken from each lot of 200 or fewer. The flat steel from which two specimens are to be removed must receive the same heat treatment as the spheres themselves. Samples must be removed after heat treatment as illustrated in appendix A to this subpart.
(2) Specimens must comply with the following:
(i) When a cylinder wall is 3/16 inch thick or less, one the following gauge lengths is authorized: A gauge length of 8 inches with a width not over 1 1/2 inches, a gauge length of 2 inches with a width not over 1 1/2 inches, or a gauge length at least twenty-four (24) times the thickness with a width not over six (6) times the thickness.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When size of the cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show with the record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”), corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For strain measurement, the initial strain reference must be set while the specimen is under a stress of 12,000 psig, and the strain indicator reading must be set at the calculated corresponding strain.
(k) Elongation. Mechanical test specimens must show at least a 40 percent elongation for a 2-inch gauge length or at least 20 percent in other cases. However, elongation percentages may be reduced numerically by 2 percent for 2-inch specimens, and by 1 percent in other cases, for each 7,500 psig increase of tensile strength above 50,000 psig. The tensile strength may be incrementally increased by four increments of 7,500 psig for a maximum total of 30,000 psig.
(l) Tests of welds. Except for brazed seams, welds must be tested as follows:
(1) Tensile test. A specimen must be removed from one cylinder of each lot of 200 or fewer, or welded test plate. The welded test plate must be of one of the heats in the lot of 200 or fewer which it represents, in the same condition and approximately the same thickness as the cylinder wall except that in no case must it be of a lesser thickness than that required for a quarter size Charpy impact specimen. The weld must be made by the same procedures and subjected to the same heat treatment as the major weld on the cylinder. The specimen must be taken from across the major seam and must be prepared and tested in conformance with and must meet the requirements of CGA C-3. Should this specimen fail to meet the requirements, one additional specimen must be taken from two additional cylinders or welded test plates from the same lot and tested. If either of these latter two specimens fail to meet the requirements, the entire lot represented must be rejected.
(2) Guided bend test. A root bend test specimen must be removed from the cylinder or welded test plate that was used for the tensile test specified in paragraph (l)(1) of this section. The specimen must be taken from across the circumferential seam and must be prepared and tested in conformance with and must meet the requirements of CGA C-3. Should this specimen fail to meet the requirements, one additional specimen must be taken from two additional cylinders or welded test plates from the same lot and tested. If either of these latter two specimens fail to meet the requirements, the entire lot represented must be rejected.
(3) Alternate guided-bend test. This test may be used and must be as required by CGA C-3. The specimen must be bent until the elongation at the outer surface, adjacent to the root of the weld, between the lightly scribed gage lines a to b, must be at least 20 percent, except that this percentage may be reduced for steels having a tensile strength in excess of 50,000 psig, as provided in paragraph (k) of this section. Should the specimen fail to meet the requirements, one additional specimen must be taken from two additional cylinders or welded test plates from the same lot and tested. If any of these latter two specimens fail to meet the requirements, the entire lot represented must be rejected.
(m) Rejected cylinders. Reheat treatment is authorized for a rejected cylinder in accordance with this paragraph (m). After reheat, a cylinder must pass all prescribed tests in this section to be acceptable. Repair of brazed seams by brazing and welded seams by welding is considered authorized. For cylinders with an outside diameter of less than or equal to six (6) inches, welded seam repairs greater than one (1) inch in length shall require reheat treatment of the cylinder. For cylinders greater than an outside diameter of six (6) inches, welded seam repairs greater than three (3) inches in length shall require reheat treatment.
(n) Markings. (1) Markings must be as required in § 178.35 and in addition must be stamped plainly and permanently in one of the following locations on the cylinder:
(i) On shoulders and top heads whose wall thickness is not less than 0.087 inch thick;
(ii) On side wall adjacent to top head for side walls not less than 0.090 inch thick;
(iii) On a cylindrical portion of the shell that extends beyond the recessed bottom of the cylinder constituting an integral and non-pressure part of the cylinder;
(iv) On a plate attached to the top of the cylinder or permanent part thereof; sufficient space must be left on the plate to provide for stamping at least six retest dates; the plate must be at least 1/16 inch thick and must be attached by welding, or by brazing at a temperature of at least 1100 °F., throughout all edges of the plate;
(v) On the neck, neckring, valve boss, valve protection sleeve, or similar part permanently attached to the top of the cylinder; or
(vi) On the footring permanently attached to the cylinder, provided the water capacity of the cylinder does not exceed 30 pounds.
(2) [Reserved]
§ 178.53   Specification 4D welded steel cylinders for aircraft use.
(a) Type, size, and service pressure. A DOT 4D cylinder is a welded steel sphere (two seamless hemispheres) or circumferentially welded cylinder (two seamless drawn shells) with a water capacity not over 100 pounds and a service pressure of at least 300 but not over 500 psig. Cylinders closed in by spinning process are not authorized.
(b) Steel. Open-hearth or electric steel of uniform and weldable quality must be used. Content may not exceed the following: Carbon, 0.25; phosphorus, 0.045; sulphur, 0.050, except that the following steels commercially known as 4130X and Type 304, 316, 321, and 347 stainless steels may be used with proper welding procedure. A heat of steel made under table 1 in this paragraph (b), check chemical analysis of which is slightly out of the specified range, is acceptable, if satisfactory in all other respects, provided the tolerances shown in table 2 in this paragraph (b) are not exceeded, except as approved by the Associate Administrator. The following chemical analyses are authorized:
Table 1—4130X Steel
Table 2—Authorized Stainless Steels
1 Titanium may not be less than 5C and not more than 0.60%.
2 Columbium may not be less than 10C and not more than 1.0%.
Table 3—Check Analysis Tolerances
1 Rephosphorized steels not subject to check analysis for phosphorus.
(c) Identification of material. Material must be identified by any suitable method except that plates and billets for hotdrawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished container appreciably. A reasonably smooth and uniform surface finish is required. Welding procedures and operators must be qualified in accordance with CGA Pamphlet C-3 (IBR, see § 171.7 of this subchapter).
(e) Wall thickness. The wall stress at the minimum test pressure may not exceed 24,000 psi, except where steels commercially known as 4130X, types 304, 316, 321, and 347 stainless steels are used, stress at the test pressures may not exceed 37,000 psi. The minimum wall thickness for any container having a capacity of 1,100 cubic inches or less is 0.04 inch. The minimum wall thickness for any container having a capacity in excess of 1,100 cubic inches is 0.095 inch. Calculations must be done by the following:
(1) Calculation for a “sphere” must be made by the formula:
(2) Calculation for a cylinder must be made by the formula:
(f) Heat treatment. The completed cylinders must be uniformly and properly heat-treated prior to tests.
(g) Openings in container. Openings in cylinders must comply with the following:
(1) Each opening in the container, except those for safety devices, must be provided with a fitting, boss, or pad, securely attached to the container by brazing or by welding or by threads. If threads are used, they must comply with the following:
(i) Threads must be clean cut, even, without checks, and tapped to gauge.
(ii) Taper threads must be of a length not less than that specified for American Standard taper pipe threads.
(iii) Straight threads, having at least 4 engaged threads, must have a tight fit and calculated shear strength of at least 10 times the test pressure of the container. Gaskets, adequate to prevent leakage, are required.
(2) Closure of a fitting, boss, or pad must be adequate to prevent leakage.
(h) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) Lot testing. (i) At least one cylinder selected at random out of each lot of 200 or fewer must be tested by water-jacket or direct expansion as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) The selected cylinder must be tested to a minimum of three (3) times service pressure.
(iii) The minimum test pressure must be maintained be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(2) Pressure testing. (i) The remaining cylinders in each lot must be tested by the proof pressure water-jacket or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. Further, all testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1. Determination of expansion properties is not required.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure and show no defect. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2, as appropriate.
(3) Alternative volumetric expansion testing. As an alternative to the testing prescribed in paragraphs (h)(1) and (2) of this section, every cylinder may be volumetrically expansion tested by the water jacket or direct expansion test method. The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(i) Each cylinder must be tested to a minimum of at least two (2) times its service pressure.
(ii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and previous to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iii) Permanent volumetric expansion may not exceed 10 percent of total volumetric expansion at test pressure.
(i) Flattening test for spheres and cylinders. Spheres and cylinders must be subjected to a flattening test as follows:
(1) One sphere taken at random out of each lot of 200 or less must be subjected to a flattening test as follows:
(i) The test must be performed after the hydrostatic test.
(ii) The test must be between parallel steel plates on a press with a welded seam at right angles to the plates. Any projecting appurtenances may be cut off (by mechanical means only) prior to crushing.
(2) One cylinder taken at random out of each lot of 200 or less must be subjected to a flattening test, as follows:
(i) The test must be performed after the hydrostatic test.
(ii) The test must be between knife edges, wedge shaped, 60° angle, rounded to 1/2 inch radius. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to the same heat treatment as the finished cylinder.
(j) Physical test and specimens for spheres and cylinders. Spheres and cylinders must be subjected to a physical test as follows:
(1) Physical test for spheres are required on 2 specimens cut from a flat representative sample plate of the same heat taken at random from the steel used to produce the sphere. This flat steel from which the 2 specimens are to be cut must receive the same heat-treatment as the spheres themselves. Sample plates must be taken for each lot of 200 or less spheres.
(2) Specimens for spheres must have a gauge length 2 inches with a width not over 1 1/2 inches, or a gauge length at least 24 times the thickness with a width not over 6 times the thickness is authorized when a wall is not over 3/16 inch thick.
(3) Physical test for cylinders is required on 2 specimens cut from 1 cylinder taken at random out of each lot of 200 or less. For lots of 30 or less, physical tests are authorized to be made on a ring at least 8 inches long cut from each cylinder and subjected to the same heat treatment as the finished cylinder.
(4) Specimens for cylinders must conform to the following:
(i) A gauge length of 8 inches with a width not over 1 1/2 inches, or a gauge length of 2 inches with a width not over 1 1/2 inches, or a gauge length at least 24 times the thickness with a width not over 6 times the thickness is authorized when a cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within 1 inch of each end of the reduced section. Heating of the specimen for any purpose is not authorized.
(5) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi and the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(k) Acceptable results for physical and flattening tests. Either of the following is an acceptable result:
(1) An elongation of at least 40 percent for a 2 inch gauge length or at least 20 percent in other cases and yield strength not over 73 percent of tensile strength. In this instance, the flattening test is not required.
(2) An elongation of at least 20 percent for a 2 inch gauge length or 10 percent in other cases. Flattening is required to 50 percent of the original outside diameter without cracking.
(l) Rejected cylinders. Reheat-treatment is authorized for rejected cylinders. Subsequent thereto, containers must pass all prescribed tests to be acceptable. Repair of welded seams by welding prior to reheat-treatment is authorized.
(m) Marking. Marking on each container by stamping plainly and permanently are only authorized where the metal is at least 0.09 inch thick, or on a metal nameplate permanently secured to the container by means other than soft solder, or by means that would not reduce the wall thickness.
§ 178.55   Specification 4B240ET welded or brazed cylinders.
(a) Type, spinning process, size and service pressure. A DOT 4B240ET cylinder is a brazed type cylinder made from electric resistance welded tubing. The maximum water capacity of this cylinder is 12 pounds or 333 cubic inches and the service must be 240 psig. The maximum outside diameter of the shell must be five inches and maximum length of the shell is 21 inches. Cylinders closed in by a spinning process are authorized.
(b) Steel. Open-hearth, basic oxygen, or electric steel of uniform quality must be used. Plain carbon steel content may not exceed the following: Carbon, 0.25; phosphorus, 0.045; sulfur, 0.050. The addition of other elements for alloying effect is prohibited.
(c) Identification of material. Material must be identified by any suitable method.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. Heads may be attached to shells by lap brazing or may be formed integrally. The thickness of the bottom of cylinders welded or formed by spinning is, under no condition, to be less than two times the minimum wall thickness of the cylindrical shell. Such bottom thicknesses must be measured within an area bounded by a line representing the points of contact between the cylinder and the floor when the cylinder is in a vertical position. Seams must conform to the following:
(1) Circumferential seams must be by brazing only. Heads must be attached to shells by the lap brazing method and must overlap not less than four times the wall thickness. Brazing material must have a melting point of not less than 1000 °F. Heads must have a driving fit with the shell unless the shell is crimped, swedged, or curled over the skirt or flange of the head and be thoroughly brazed until complete penetration of the joint by the brazing material is secured. Brazed joints may be repaired by brazing.
(2) Longitudinal seams in shell must be by electric resistance welded joints only. No repairs to longitudinal joints is permitted.
(3) Welding procedures and operators must be qualified in accordance with CGA C-3 (IBR, see § 171.7 of this subchapter).
(e) Welding or brazing. Only the attachment, by welding or brazing, to the tops and bottoms of cylinders of neckrings, footrings, handles, bosses, pads, and valve protection rings is authorized. Provided that such attachments and the portion of the container to which they are attached are made of weldable steel, the carbon content of which may not exceed 0.25 percent.
(f) Wall thickness. The wall stress must be at least two times the service pressure and may not exceed 18,000 psi. The minimum wall thickness is 0.044 inch. Calculation must be made by the following formula:
(g) Heat treatment. Heads formed by drawing or pressing must be uniformly and properly heat treated prior to tests. Cylinders with integral formed heads or bases must be subjected to a normalizing operation. Normalizing and brazing operations may be combined, provided the operation is carried out at a temperature in excess of the upper critical temperature of the steel.
(h) Openings in cylinders. Openings in cylinders must comply with the following:
(1) Each opening in cylinders, except those for safety devices, must be provided with a fitting, boss, or pad, securely attached to the cylinder by brazing or by welding or by threads. A fitting, boss, or pad must be of steel suitable for the method of attachment employed, and which need not be identified or verified as to analysis, except that if attachment is by welding, carbon content may not exceed 0.25 percent. If threads are used, they must comply with the following:
(i) Threads must be clean cut, even without checks, and tapped to gauge.
(ii) Taper threads to be of length not less than as specified for American Standard taper pipe threads.
(iii) Straight threads, having at least 4 engaged threads, to have tight fit and calculated shear strength at least 10 times the test pressure of the cylinder; gaskets required, adequate to prevent leakage.
(2) Closure of a fitting, boss, or pad must be adequate to prevent leakage.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) Lot testing. (i) At least one (1) cylinder selected at random out of each lot of 200 or fewer must be tested by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure.
(iii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(2) Pressure testing. (i) The remaining cylinders in each lot must be tested by the proof pressure water-jacket or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure and show no defect. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2. Determination of expansion properties is not required.
(3) Burst testing. (i) For purposes of burst testing, each 1,000 cylinders or fewer successively produced each day constitutes a lot. All cylinders of a lot must be of identical size, construction heat treatment, finish, and quality.
(ii) One cylinder must be selected from each lot and be hydrostatically pressure tested to destruction. If this cylinder bursts below five (5) times the service pressure, then two additional cylinders from the same lot as the previously tested cylinder must be selected and subjected to this test. If either of these cylinders fails by bursting below five (5) times the service pressure then the entire lot must be rejected. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) Lot testing. (i) At least one (1) cylinder selected at random out of each lot of 200 or fewer must be tested by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure.
(iii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(2) Pressure testing. (i) The remaining cylinders in each lot must be tested by the proof pressure water-jacket or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure and show no defect. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2. Determination of expansion properties is not required.
(3) Burst testing. (i) For purposes of burst testing, each 1,000 cylinders or fewer successively produced each day constitutes a lot. All cylinders of a lot must be of identical size, construction heat treatment, finish, and quality.
(ii) One cylinder must be selected from each lot and be hydrostatically pressure tested to destruction. If this cylinder bursts below five (5) times the service pressure, then two additional cylinders from the same lot as the previously tested cylinder must be selected and subjected to this test. If either of these cylinders fails by bursting below five (5) times the service pressure then the entire lot must be rejected. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(j) Flattening test. Following the hydrostatic test, one cylinder taken at random out of each lot of 200 or less, must be subjected to a flattening test that is between knife edges, wedge shaped, 60° angle, rounded to 1/2 inch radius.
(k) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material, as follows:
(1) The test is required on 2 specimens cut from 1 cylinder, or part thereof heat-treated as required, taken at random out of each lot of 200 or less in the case of cylinders of capacity greater than 86 cubic inches and out of each lot of 500 or less for cylinders having a capacity of 86 cubic inches or less.
(2) Specimens must conform to the following:
(i) A gauge length of 8 inches with a width not over 1 1/2 inches, a gauge length of 2 inches with a width not over 1 1/2 inches, or a gauge length at least 24 times the thickness with a width not over 6 times the thickness is authorized when a cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”) corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain must be set while the specimen is under a stress of 12,000 psi and the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(l) Acceptable results for physical and flattening tests. Acceptable results for the physical and flattening tests are an elongation of at least 40 percent for a 2 inch gauge length or at least 20 percent in other cases and a yield strength not over 73 percent of tensile strength. In this instance the flattening test is required, without cracking, to six times the wall thickness with a weld 90° from the direction of the applied load. Two rings cut from the ends of length of pipe used in production of a lot may be used for the flattening test provided the rings accompany the lot which they represent in all thermal processing operations. At least one of the rings must pass the flattening test.
(m) Leakage test. All spun cylinders and plugged cylinders must be tested for leakage by gas or air pressure after the bottom has been cleaned and is free from all moisture, subject to the following conditions:
(1) Pressure, approximately the same as but no less than service pressure, must be applied to one side of the finished bottom over an area of at least 1/16 of the total area of the bottom but not less than 3/4 inch in diameter, including the closure, for at least 1 minute, during which time the other side of the bottom exposed to pressure must be covered with water and closely examined for indications of leakage. Except as provided in paragraph (n) of this section, cylinders which are leaking must be rejected.
(2) A spun cylinder is one in which an end closure in the finished cylinder has been welded by the spinning process.
(3) A plugged cylinder is one in which a permanent closure in the bottom of a finished cylinder has been effected by a plug.
(4) As a safety precaution, if the manufacturer elects to make this test before the hydrostatic test, he should design his apparatus so that the pressure is applied to the smallest area practicable, around the point of closure, and so as to use the smallest possible volume of air or gas.
(n) Rejected cylinders. Repairs of rejected cylinders is authorized. Cylinders that are leaking must be rejected, except that:
(1) Spun cylinders rejected under the provisions of paragraph (m) of this section may be removed from the spun cylinder category by drilling to remove defective material, tapping, and plugging.
(2) Brazed joints may be rebrazed.
(3) Subsequent to the operations noted in paragraphs (n)(1) and (n)(2) of this section, acceptable cylinders must pass all prescribed tests.
(o) Marking. Markings on each cylinder must be by stamping plainly and permanently on shoulder, top head, neck or valve protection collar which is permanently attached to the cylinders and forming an integral part thereof, provided that cylinders not less than 0.090 inch thick may be stamped on the side wall adjacent to top head.
§ 178.56   Specification 4AA480 welded steel cylinders.
(a) Type, size, and service pressure. A DOT 4AA480 cylinder is a welded steel cylinder having a water capacity (nominal) not over 1,000 pounds water capacity and a service pressure of 480 psig. Closures welded by spinning process not permitted.
(b) Steel. The limiting chemical composition of steel authorized by this specification must be as shown in table I of appendix A to this part.
(c) Identification of material. Material must be identified by any suitable method except that plates and billets for hotdrawn cylinders must be marked with the heat number.
(d) Manufacture. Cylinders must be manufactured using equipment and processes adequate to ensure that each cylinder produced conforms to the requirements of this subpart. No defect is permitted that is likely to weaken the finished cylinder appreciably. A reasonably smooth and uniform surface finish is required. Exposed bottom welds on cylinders over 18 inches long must be protected by footrings. Minimum thickness of heads and bottoms may not be less than 90 percent of the required thickness of the side wall. Seams must be made as follows:
(1) Circumferential seams must be welded. Brazing is not authorized.
(2) Longitudinal seams are not permitted.
(3) Welding procedures and operators must be qualified in accordance with CGA C-3 (IBR, see § 171.7 of this subchapter).
(e) Welding. Only the welding of neckrings, footrings, bosses, pads, and valve protection rings to the tops and bottoms of cylinders is authorized. Provided that such attachments are made of weldable steel, the carbon content of which does not exceed 0.25 percent.
(f) Wall thickness. The wall thickness of the cylinder must conform to the following:
(1) For cylinders with an outside diameter over 5 inches, the minimum wall thickness is 0.078 inch. In any case, the minimum wall thickness must be such that the calculated wall stress at the minimum test pressure (in paragraph (i) of this section) may not exceed the lesser value of either of the following:
(i) One-half of the minimum tensile strength of the material determined as required in paragraph (j) of this section; or
(ii) 35,000 psi.
(2) Calculation must be made by the formula:
(3) The ratio of tangential length to outside diameter may not exceed 4.0 for cylinders with a wall thickness less than 0.100 inch.
(g) Heat treatment. Each cylinder must be uniformly and properly heat treated prior to tests. Any suitable heat treatment in excess of 1100 °F is authorized except that liquid quenching is not permitted. Heat treatment must be accomplished after all forming and welding operations. Heat treatment is not required after welding weldable low carbon parts to attachments of similar material which have been previously welded to the top or bottom of cylinders and properly heat treated, provided such subsequent welding does not produce a temperature in excess of 400 °F., in any part of the top or bottom material.
(h) Openings in cylinders. Openings in cylinders must conform to the following:
(1) All openings must be in the heads or bases.
(2) Each opening in the cylinder, except those for safety devices, must be provided with a fitting boss, or pad, securely attached to the cylinder by welding or by threads. If threads are used they must comply with the following:
(i) Threads must be clean-cut, even without checks and cut to gauge.
(ii) Taper threads to be of length not less than as specified for American Standard taper pipe threads.
(iii) Straight threads having at least 6 engaged threads, must have a tight fit and a calculated shear strength at least 10 times the test pressure of the cylinder. Gaskets, adequate to prevent leakage, are required.
(3) Closure of a fitting, boss or pad must be adequate to prevent leakage.
(i) Pressure testing. Each cylinder must successfully withstand a pressure test as follows:
(1) Lot testing. (i) At least one (1) cylinder selected at random out of each lot of 200 or fewer must be tested by water-jacket or direct expansion method as prescribed in CGA C-1 (IBR; see § 171.7 of this subchapter). The testing equipment must be calibrated as prescribed in CGA C-1. All testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) The selected cylinder must be tested to a minimum of two (2) times service pressure.
(iii) The minimum test pressure must be maintained at least 30 seconds and sufficiently longer to ensure complete expansion. Any internal pressure applied after heat-treatment and prior to the official test may not exceed 90 percent of the test pressure. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1, section 5.7.2.
(iv) Permanent volumetric expansion may not exceed 10 percent of the total volumetric expansion at test pressure.
(v) If the selected cylinder fails, then two (2) additional specimens must be selected at random from the same lot and subjected to the prescribed testing. If either of these fails the test, then each cylinder in that lot must be tested as prescribed in paragraph (i)(l) of this section.
(2) Pressure testing. (i) The remaining cylinders in each lot must be tested by the proof pressure, water-jacket, or direct expansion test method as prescribed in CGA C-1. The minimum test pressure must be maintained for the specific timeframe and the testing equipment must be calibrated as prescribed in CGA C-1. Further, all testing equipment and pressure indicating devices must be accurate within the parameters defined in CGA C-1.
(ii) Each cylinder must be tested to a minimum of two (2) times service pressure and show no defect. A cylinder showing a defect must be rejected unless it may be requalified under paragraph (m) of this section. If, due to failure of the test apparatus or operator error, the test pressure cannot be maintained, the test may be repeated in accordance with CGA C-1 5.7.2 or 7.1.2, as appropriate. Determination of expansion properties is not required.
(j) Physical test. A physical test must be conducted to determine yield strength, tensile strength, elongation, and reduction of area of material, as follows:
(1) The test is required on 2 specimens cut from one cylinder having passed the hydrostatic test, or part thereof heat-treated as required, taken at random out of each lot of 200 or less.
(2) Specimens must conform to the following:
(i) A gauge length of 8 inches with a width not over 1 1/2 inches, a gauge length of 2 inches with a width not over 1 1/2 inches, or a gauge length at least 24 times the thickness with a width not over 6 times thickness is authorized when the cylinder wall is not over 3/16 inch thick.
(ii) The specimen, exclusive of grip ends, may not be flattened. Grip ends may be flattened to within one inch of each end of the reduced section.
(iii) When size of cylinder does not permit securing straight specimens, the specimens may be taken in any location or direction and may be straightened or flattened cold, by pressure only, not by blows. When specimens are so taken and prepared, the inspector's report must show in connection with record of physical tests detailed information in regard to such specimens.
(iv) Heating of a specimen for any purpose is not authorized.
(3) The yield strength in tension must be the stress corresponding to a permanent strain of 0.2 percent of the gauge length. The following conditions apply:
(i) The yield strength must be determined by either the “offset” method or the “extension under load” method as prescribed in ASTM E 8 (IBR, see § 171.7 of this subchapter).
(ii) In using the “extension under load” method, the total strain (or “extension under load”), corresponding to the stress at which the 0.2 percent permanent strain occurs may be determined with sufficient accuracy by calculating the elastic extension of the gauge length under appropriate load and adding thereto 0.2 percent of the gauge length. Elastic extension calculations must be based on an elastic modulus of 30,000,000. In the event of controversy, the entire stress-strain diagram must be plotted and the yield strength determined from the 0.2 percent offset.
(iii) For the purpose of strain measurement, the initial strain reference must be set while the specimen is under a stress of 12,000 psi and the strain indicator reading being set at the calculated corresponding strain.
(iv) Cross-head speed of the testing machine may not exceed 1/8 inch per minute during yield strength determination.
(k) Elongation. Physical test specimens must show at least a 40 percent elongation for 2-inch gauge lengths or at least a 20 percent elongation in other cases. Except that these elongation percentages may be reduced numerically by 2 for 2-inch specimens and by 1 in other cases for each 7,500 psi increment of tensile strength above 50,000 psi to a maximum of four such increments.
(l) Tests of welds. Welds must be tested as follows:
(1) Tensile test. A specimen must be cut from one cylinder of each lot of 200 or less, or a welded test plate. The welded test plate must be of one of the heats in the lot of 200 or less which it represents, in the same condition and approximately the same thickness as the cylinder wall except that it may not be of a lesser thickness than that required for a quarter size Charpy impact specimen. The weld must be made by the same procedures and subjected to the same heat treatment as the major weld on the cylinder. The specimens must be taken across the major seam and must be prepared and tested in accordance with and must meet the requirements of CGA Pamphlet C-3. Should this specimen fail to meet the requirements, specimens may be taken from two additional cylinders or welded test plates from the same lot and tested. If either of the latter specimens fail to meet the requirements, the entire lot represented must be rejected.
(2) Guided bend test. A root bend test specimen must be cut from the cylinder or a welded test plate, used for the tensile test specified in paragraph (l)(1) of this section. Specimens must be taken from across the major seam and must be prepared and tested in accordance with and must meet the requirements of CGA Pamphlet C-3.
(3) Alternate guided-bend test. This test may be used and must be as required by CGA Pamphlet C-3. The specimen must be bent until the elongation at the outer surface, adjacent to the root of the weld, between the lightly scribed gage lines-a to b, is at least 20 percent, except that this percentage may be reduced for steels having a tensile strength in excess of 50,000 psi, as provided in paragraph (k) of this section.
(m) Rejected cylinders. Reheat treatment of rejected cylinders is authorized. Subsequent thereto, cylinders must pass all prescribed tests to be acceptable. Repair of welded seams by welding is authorized.
(n) Markings. Markings must be stamped plainly and permanently in one of the following locations on the cylinder:
(1) On shoulders and top heads not less than 0.087 inch thick.
(2) On neck, valve boss, valve protection sleeve, or similar part permanently attached to top end of cylinder.
(3) On a plate attached to the top of the cylinder or permanent part thereof: sufficient space must be left on the plate to provide for stamping at least six retest dates: the plate must be at least 1/16 inch thick and must be attached by welding or by brazing at a temperature of at least 1100 °F, throughout all edges of the plate.
(4) Variations in location of markings authorized only when necessitated by lack of space.